Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 asm changes from Ingo Molnar:
 "There were lots of changes in this development cycle:

   - over 100 separate cleanups, restructuring changes, speedups and
     fixes in the x86 system call, irq, trap and other entry code, part
     of a heroic effort to deobfuscate a decade old spaghetti asm code
     and its C code dependencies (Denys Vlasenko, Andy Lutomirski)

   - alternatives code fixes and enhancements (Borislav Petkov)

   - simplifications and cleanups to the compat code (Brian Gerst)

   - signal handling fixes and new x86 testcases (Andy Lutomirski)

   - various other fixes and cleanups

  By their nature many of these changes are risky - we tried to test
  them well on many different x86 systems (there are no known
  regressions), and they are split up finely to help bisection - but
  there's still a fair bit of residual risk left so caveat emptor"

* 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (148 commits)
  perf/x86/64: Report regs_user->ax too in get_regs_user()
  perf/x86/64: Simplify regs_user->abi setting code in get_regs_user()
  perf/x86/64: Do report user_regs->cx while we are in syscall, in get_regs_user()
  perf/x86/64: Do not guess user_regs->cs, ss, sp in get_regs_user()
  x86/asm/entry/32: Tidy up JNZ instructions after TESTs
  x86/asm/entry/64: Reduce padding in execve stubs
  x86/asm/entry/64: Remove GET_THREAD_INFO() in ret_from_fork
  x86/asm/entry/64: Simplify jumps in ret_from_fork
  x86/asm/entry/64: Remove a redundant jump
  x86/asm/entry/64: Optimize [v]fork/clone stubs
  x86/asm/entry: Zero EXTRA_REGS for stub32_execve() too
  x86/asm/entry/64: Move stub_x32_execvecloser() to stub_execveat()
  x86/asm/entry/64: Use common code for rt_sigreturn() epilogue
  x86/asm/entry/64: Add forgotten CFI annotation
  x86/asm/entry/irq: Simplify interrupt dispatch table (IDT) layout
  x86/asm/entry/64: Move opportunistic sysret code to syscall code path
  x86, selftests: Add sigreturn selftest
  x86/alternatives: Guard NOPs optimization
  x86/asm/entry: Clear EXTRA_REGS for all executable formats
  x86/signal: Remove pax argument from restore_sigcontext
  ...

6 files changed, 760 insertions, 0 deletions

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index d643d5242537..95abddcd7839 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -17,6 +17,7 @@ TARGETS += sysctl
 TARGETS += timers
 TARGETS += user
 TARGETS += vm
+TARGETS += x86
 #Please keep the TARGETS list alphabetically sorted
 
 TARGETS_HOTPLUG = cpu-hotplug
diff --git a/tools/testing/selftests/x86/.gitignore b/tools/testing/selftests/x86/.gitignore
new file mode 100644
index 000000000000..15034fef9698
--- /dev/null
+++ b/tools/testing/selftests/x86/.gitignore
@@ -0,0 +1,2 @@
+*_32
+*_64
diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
new file mode 100644
index 000000000000..f0a7918178dd
--- /dev/null
+++ b/tools/testing/selftests/x86/Makefile
@@ -0,0 +1,48 @@
+.PHONY: all all_32 all_64 check_build32 clean run_tests
+
+TARGETS_C_BOTHBITS := sigreturn
+
+BINARIES_32 := $(TARGETS_C_BOTHBITS:%=%_32)
+BINARIES_64 := $(TARGETS_C_BOTHBITS:%=%_64)
+
+CFLAGS := -O2 -g -std=gnu99 -pthread -Wall
+
+UNAME_P := $(shell uname -p)
+
+# Always build 32-bit tests
+all: all_32
+
+# If we're on a 64-bit host, build 64-bit tests as well
+ifeq ($(shell uname -p),x86_64)
+all: all_64
+endif
+
+all_32: check_build32 $(BINARIES_32)
+
+all_64: $(BINARIES_64)
+
+clean:
+        $(RM) $(BINARIES_32) $(BINARIES_64)
+
+run_tests:
+        ./run_x86_tests.sh
+
+$(TARGETS_C_BOTHBITS:%=%_32): %_32: %.c
+        $(CC) -m32 -o $@ $(CFLAGS) $(EXTRA_CFLAGS) $^ -lrt -ldl
+
+$(TARGETS_C_BOTHBITS:%=%_64): %_64: %.c
+        $(CC) -m64 -o $@ $(CFLAGS) $(EXTRA_CFLAGS) $^ -lrt -ldl
+
+check_build32:
+        @if ! $(CC) -m32 -o /dev/null trivial_32bit_program.c; then     \
+          echo "Warning: you seem to have a broken 32-bit build" 2>&1;  \
+          echo "environment.  If you are using a Debian-like";          \
+          echo " distribution, try:";                                   \
+          echo "";                                                      \
+          echo "  apt-get install gcc-multilib libc6-i386 libc6-dev-i386"; \
+          echo "";                                                      \
+          echo "If you are using a Fedora-like distribution, try:";     \
+          echo "";                                                      \
+          echo "  yum install glibc-devel.*i686";                       \
+          exit 1;                                                       \
+        fi
diff --git a/tools/testing/selftests/x86/run_x86_tests.sh b/tools/testing/selftests/x86/run_x86_tests.sh
new file mode 100644
index 000000000000..3d3ec65f3e7c
--- /dev/null
+++ b/tools/testing/selftests/x86/run_x86_tests.sh
@@ -0,0 +1,11 @@
+#!/bin/bash
+
+# This is deliberately minimal.  IMO kselftests should provide a standard
+# script here.
+./sigreturn_32 || exit 1
+
+if [[ "$uname -p" -eq "x86_64" ]]; then
+    ./sigreturn_64 || exit 1
+fi
+
+exit 0
diff --git a/tools/testing/selftests/x86/sigreturn.c b/tools/testing/selftests/x86/sigreturn.c
new file mode 100644
index 000000000000..b5aa1bab7416
--- /dev/null
+++ b/tools/testing/selftests/x86/sigreturn.c
@@ -0,0 +1,684 @@
+/*
+ * sigreturn.c - tests for x86 sigreturn(2) and exit-to-userspace
+ * Copyright (c) 2014-2015 Andrew Lutomirski
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * This is a series of tests that exercises the sigreturn(2) syscall and
+ * the IRET / SYSRET paths in the kernel.
+ *
+ * For now, this focuses on the effects of unusual CS and SS values,
+ * and it has a bunch of tests to make sure that ESP/RSP is restored
+ * properly.
+ *
+ * The basic idea behind these tests is to raise(SIGUSR1) to create a
+ * sigcontext frame, plug in the values to be tested, and then return,
+ * which implicitly invokes sigreturn(2) and programs the user context
+ * as desired.
+ *
+ * For tests for which we expect sigreturn and the subsequent return to
+ * user mode to succeed, we return to a short trampoline that generates
+ * SIGTRAP so that the meat of the tests can be ordinary C code in a
+ * SIGTRAP handler.
+ *
+ * The inner workings of each test is documented below.
+ *
+ * Do not run on outdated, unpatched kernels at risk of nasty crashes.
+ */
+
+#define _GNU_SOURCE
+
+#include <sys/time.h>
+#include <time.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include <sys/mman.h>
+#include <sys/signal.h>
+#include <sys/ucontext.h>
+#include <asm/ldt.h>
+#include <err.h>
+#include <setjmp.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <sys/ptrace.h>
+#include <sys/user.h>
+
+/*
+ * In principle, this test can run on Linux emulation layers (e.g.
+ * Illumos "LX branded zones").  Solaris-based kernels reserve LDT
+ * entries 0-5 for their own internal purposes, so start our LDT
+ * allocations above that reservation.  (The tests don't pass on LX
+ * branded zones, but at least this lets them run.)
+ */
+#define LDT_OFFSET 6
+
+/* An aligned stack accessible through some of our segments. */
+static unsigned char stack16[65536] __attribute__((aligned(4096)));
+
+/*
+ * An aligned int3 instruction used as a trampoline.  Some of the tests
+ * want to fish out their ss values, so this trampoline copies ss to eax
+ * before the int3.
+ */
+asm (".pushsection .text\n\t"
+     ".type int3, @function\n\t"
+     ".align 4096\n\t"
+     "int3:\n\t"
+     "mov %ss,%eax\n\t"
+     "int3\n\t"
+     ".size int3, . - int3\n\t"
+     ".align 4096, 0xcc\n\t"
+     ".popsection");
+extern char int3[4096];
+
+/*
+ * At startup, we prepapre:
+ *
+ * - ldt_nonexistent_sel: An LDT entry that doesn't exist (all-zero
+ *   descriptor or out of bounds).
+ * - code16_sel: A 16-bit LDT code segment pointing to int3.
+ * - data16_sel: A 16-bit LDT data segment pointing to stack16.
+ * - npcode32_sel: A 32-bit not-present LDT code segment pointing to int3.
+ * - npdata32_sel: A 32-bit not-present LDT data segment pointing to stack16.
+ * - gdt_data16_idx: A 16-bit GDT data segment pointing to stack16.
+ * - gdt_npdata32_idx: A 32-bit not-present GDT data segment pointing to
+ *   stack16.
+ *
+ * For no particularly good reason, xyz_sel is a selector value with the
+ * RPL and LDT bits filled in, whereas xyz_idx is just an index into the
+ * descriptor table.  These variables will be zero if their respective
+ * segments could not be allocated.
+ */
+static unsigned short ldt_nonexistent_sel;
+static unsigned short code16_sel, data16_sel, npcode32_sel, npdata32_sel;
+
+static unsigned short gdt_data16_idx, gdt_npdata32_idx;
+
+static unsigned short GDT3(int idx)
+{
+        return (idx << 3) | 3;
+}
+
+static unsigned short LDT3(int idx)
+{
+        return (idx << 3) | 7;
+}
+
+/* Our sigaltstack scratch space. */
+static char altstack_data[SIGSTKSZ];
+
+static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
+                       int flags)
+{
+        struct sigaction sa;
+        memset(&sa, 0, sizeof(sa));
+        sa.sa_sigaction = handler;
+        sa.sa_flags = SA_SIGINFO | flags;
+        sigemptyset(&sa.sa_mask);
+        if (sigaction(sig, &sa, 0))
+                err(1, "sigaction");
+}
+
+static void clearhandler(int sig)
+{
+        struct sigaction sa;
+        memset(&sa, 0, sizeof(sa));
+        sa.sa_handler = SIG_DFL;
+        sigemptyset(&sa.sa_mask);
+        if (sigaction(sig, &sa, 0))
+                err(1, "sigaction");
+}
+
+static void add_ldt(const struct user_desc *desc, unsigned short *var,
+                    const char *name)
+{
+        if (syscall(SYS_modify_ldt, 1, desc, sizeof(*desc)) == 0) {
+                *var = LDT3(desc->entry_number);
+        } else {
+                printf("[NOTE]\tFailed to create %s segment\n", name);
+                *var = 0;
+        }
+}
+
+static void setup_ldt(void)
+{
+        if ((unsigned long)stack16 > (1ULL << 32) - sizeof(stack16))
+                errx(1, "stack16 is too high\n");
+        if ((unsigned long)int3 > (1ULL << 32) - sizeof(int3))
+                errx(1, "int3 is too high\n");
+
+        ldt_nonexistent_sel = LDT3(LDT_OFFSET + 2);
+
+        const struct user_desc code16_desc = {
+                .entry_number    = LDT_OFFSET + 0,
+                .base_addr       = (unsigned long)int3,
+                .limit           = 4095,
+                .seg_32bit       = 0,
+                .contents        = 2, /* Code, not conforming */
+                .read_exec_only  = 0,
+                .limit_in_pages  = 0,
+                .seg_not_present = 0,
+                .useable         = 0
+        };
+        add_ldt(&code16_desc, &code16_sel, "code16");
+
+        const struct user_desc data16_desc = {
+                .entry_number    = LDT_OFFSET + 1,
+                .base_addr       = (unsigned long)stack16,
+                .limit           = 0xffff,
+                .seg_32bit       = 0,
+                .contents        = 0, /* Data, grow-up */
+                .read_exec_only  = 0,
+                .limit_in_pages  = 0,
+                .seg_not_present = 0,
+                .useable         = 0
+        };
+        add_ldt(&data16_desc, &data16_sel, "data16");
+
+        const struct user_desc npcode32_desc = {
+                .entry_number    = LDT_OFFSET + 3,
+                .base_addr       = (unsigned long)int3,
+                .limit           = 4095,
+                .seg_32bit       = 1,
+                .contents        = 2, /* Code, not conforming */
+                .read_exec_only  = 0,
+                .limit_in_pages  = 0,
+                .seg_not_present = 1,
+                .useable         = 0
+        };
+        add_ldt(&npcode32_desc, &npcode32_sel, "npcode32");
+
+        const struct user_desc npdata32_desc = {
+                .entry_number    = LDT_OFFSET + 4,
+                .base_addr       = (unsigned long)stack16,
+                .limit           = 0xffff,
+                .seg_32bit       = 1,
+                .contents        = 0, /* Data, grow-up */
+                .read_exec_only  = 0,
+                .limit_in_pages  = 0,
+                .seg_not_present = 1,
+                .useable         = 0
+        };
+        add_ldt(&npdata32_desc, &npdata32_sel, "npdata32");
+
+        struct user_desc gdt_data16_desc = {
+                .entry_number    = -1,
+                .base_addr       = (unsigned long)stack16,
+                .limit           = 0xffff,
+                .seg_32bit       = 0,
+                .contents        = 0, /* Data, grow-up */
+                .read_exec_only  = 0,
+                .limit_in_pages  = 0,
+                .seg_not_present = 0,
+                .useable         = 0
+        };
+
+        if (syscall(SYS_set_thread_area, &gdt_data16_desc) == 0) {
+                /*
+                 * This probably indicates vulnerability to CVE-2014-8133.
+                 * Merely getting here isn't definitive, though, and we'll
+                 * diagnose the problem for real later on.
+                 */
+                printf("[WARN]\tset_thread_area allocated data16 at index %d\n",
+                       gdt_data16_desc.entry_number);
+                gdt_data16_idx = gdt_data16_desc.entry_number;
+        } else {
+                printf("[OK]\tset_thread_area refused 16-bit data\n");
+        }
+
+        struct user_desc gdt_npdata32_desc = {
+                .entry_number    = -1,
+                .base_addr       = (unsigned long)stack16,
+                .limit           = 0xffff,
+                .seg_32bit       = 1,
+                .contents        = 0, /* Data, grow-up */
+                .read_exec_only  = 0,
+                .limit_in_pages  = 0,
+                .seg_not_present = 1,
+                .useable         = 0
+        };
+
+        if (syscall(SYS_set_thread_area, &gdt_npdata32_desc) == 0) {
+                /*
+                 * As a hardening measure, newer kernels don't allow this.
+                 */
+                printf("[WARN]\tset_thread_area allocated npdata32 at index %d\n",
+                       gdt_npdata32_desc.entry_number);
+                gdt_npdata32_idx = gdt_npdata32_desc.entry_number;
+        } else {
+                printf("[OK]\tset_thread_area refused 16-bit data\n");
+        }
+}
+
+/* State used by our signal handlers. */
+static gregset_t initial_regs, requested_regs, resulting_regs;
+
+/* Instructions for the SIGUSR1 handler. */
+static volatile unsigned short sig_cs, sig_ss;
+static volatile sig_atomic_t sig_trapped, sig_err, sig_trapno;
+
+/* Abstractions for some 32-bit vs 64-bit differences. */
+#ifdef __x86_64__
+# define REG_IP REG_RIP
+# define REG_SP REG_RSP
+# define REG_AX REG_RAX
+
+struct selectors {
+        unsigned short cs, gs, fs, ss;
+};
+
+static unsigned short *ssptr(ucontext_t *ctx)
+{
+        struct selectors *sels = (void *)&ctx->uc_mcontext.gregs[REG_CSGSFS];
+        return &sels->ss;
+}
+
+static unsigned short *csptr(ucontext_t *ctx)
+{
+        struct selectors *sels = (void *)&ctx->uc_mcontext.gregs[REG_CSGSFS];
+        return &sels->cs;
+}
+#else
+# define REG_IP REG_EIP
+# define REG_SP REG_ESP
+# define REG_AX REG_EAX
+
+static greg_t *ssptr(ucontext_t *ctx)
+{
+        return &ctx->uc_mcontext.gregs[REG_SS];
+}
+
+static greg_t *csptr(ucontext_t *ctx)
+{
+        return &ctx->uc_mcontext.gregs[REG_CS];
+}
+#endif
+
+/* Number of errors in the current test case. */
+static volatile sig_atomic_t nerrs;
+
+/*
+ * SIGUSR1 handler.  Sets CS and SS as requested and points IP to the
+ * int3 trampoline.  Sets SP to a large known value so that we can see
+ * whether the value round-trips back to user mode correctly.
+ */
+static void sigusr1(int sig, siginfo_t *info, void *ctx_void)
+{
+        ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+        memcpy(&initial_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
+
+        *csptr(ctx) = sig_cs;
+        *ssptr(ctx) = sig_ss;
+
+        ctx->uc_mcontext.gregs[REG_IP] =
+                sig_cs == code16_sel ? 0 : (unsigned long)&int3;
+        ctx->uc_mcontext.gregs[REG_SP] = (unsigned long)0x8badf00d5aadc0deULL;
+        ctx->uc_mcontext.gregs[REG_AX] = 0;
+
+        memcpy(&requested_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
+        requested_regs[REG_AX] = *ssptr(ctx);   /* The asm code does this. */
+
+        return;
+}
+
+/*
+ * Called after a successful sigreturn.  Restores our state so that
+ * the original raise(SIGUSR1) returns.
+ */
+static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
+{
+        ucontext_t *ctx = (ucontext_t*)ctx_void;
+
+        sig_err = ctx->uc_mcontext.gregs[REG_ERR];
+        sig_trapno = ctx->uc_mcontext.gregs[REG_TRAPNO];
+
+        unsigned short ss;
+        asm ("mov %%ss,%0" : "=r" (ss));
+
+        greg_t asm_ss = ctx->uc_mcontext.gregs[REG_AX];
+        if (asm_ss != sig_ss && sig == SIGTRAP) {
+                /* Sanity check failure. */
+                printf("[FAIL]\tSIGTRAP: ss = %hx, frame ss = %hx, ax = %llx\n",
+                       ss, *ssptr(ctx), (unsigned long long)asm_ss);
+                nerrs++;
+        }
+
+        memcpy(&resulting_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
+        memcpy(&ctx->uc_mcontext.gregs, &initial_regs, sizeof(gregset_t));
+
+        sig_trapped = sig;
+}
+
+/*
+ * Checks a given selector for its code bitness or returns -1 if it's not
+ * a usable code segment selector.
+ */
+int cs_bitness(unsigned short cs)
+{
+        uint32_t valid = 0, ar;
+        asm ("lar %[cs], %[ar]\n\t"
+             "jnz 1f\n\t"
+             "mov $1, %[valid]\n\t"
+             "1:"
+             : [ar] "=r" (ar), [valid] "+rm" (valid)
+             : [cs] "r" (cs));
+
+        if (!valid)
+                return -1;
+
+        bool db = (ar & (1 << 22));
+        bool l = (ar & (1 << 21));
+
+        if (!(ar & (1<<11)))
+            return -1;  /* Not code. */
+
+        if (l && !db)
+                return 64;
+        else if (!l && db)
+                return 32;
+        else if (!l && !db)
+                return 16;
+        else
+                return -1;      /* Unknown bitness. */
+}
+
+/* Finds a usable code segment of the requested bitness. */
+int find_cs(int bitness)
+{
+        unsigned short my_cs;
+
+        asm ("mov %%cs,%0" :  "=r" (my_cs));
+
+        if (cs_bitness(my_cs) == bitness)
+                return my_cs;
+        if (cs_bitness(my_cs + (2 << 3)) == bitness)
+                return my_cs + (2 << 3);
+        if (my_cs > (2<<3) && cs_bitness(my_cs - (2 << 3)) == bitness)
+            return my_cs - (2 << 3);
+        if (cs_bitness(code16_sel) == bitness)
+                return code16_sel;
+
+        printf("[WARN]\tCould not find %d-bit CS\n", bitness);
+        return -1;
+}
+
+static int test_valid_sigreturn(int cs_bits, bool use_16bit_ss, int force_ss)
+{
+        int cs = find_cs(cs_bits);
+        if (cs == -1) {
+                printf("[SKIP]\tCode segment unavailable for %d-bit CS, %d-bit SS\n",
+                       cs_bits, use_16bit_ss ? 16 : 32);
+                return 0;
+        }
+
+        if (force_ss != -1) {
+                sig_ss = force_ss;
+        } else {
+                if (use_16bit_ss) {
+                        if (!data16_sel) {
+                                printf("[SKIP]\tData segment unavailable for %d-bit CS, 16-bit SS\n",
+                                       cs_bits);
+                                return 0;
+                        }
+                        sig_ss = data16_sel;
+                } else {
+                        asm volatile ("mov %%ss,%0" : "=r" (sig_ss));
+                }
+        }
+
+        sig_cs = cs;
+
+        printf("[RUN]\tValid sigreturn: %d-bit CS (%hx), %d-bit SS (%hx%s)\n",
+               cs_bits, sig_cs, use_16bit_ss ? 16 : 32, sig_ss,
+               (sig_ss & 4) ? "" : ", GDT");
+
+        raise(SIGUSR1);
+
+        nerrs = 0;
+
+        /*
+         * Check that each register had an acceptable value when the
+         * int3 trampoline was invoked.
+         */
+        for (int i = 0; i < NGREG; i++) {
+                greg_t req = requested_regs[i], res = resulting_regs[i];
+                if (i == REG_TRAPNO || i == REG_IP)
+                        continue;       /* don't care */
+                if (i == REG_SP) {
+                        printf("\tSP: %llx -> %llx\n", (unsigned long long)req,
+                               (unsigned long long)res);
+
+                        /*
+                         * In many circumstances, the high 32 bits of rsp
+                         * are zeroed.  For example, we could be a real
+                         * 32-bit program, or we could hit any of a number
+                         * of poorly-documented IRET or segmented ESP
+                         * oddities.  If this happens, it's okay.
+                         */
+                        if (res == (req & 0xFFFFFFFF))
+                                continue;  /* OK; not expected to work */
+                }
+
+                bool ignore_reg = false;
+#if __i386__
+                if (i == REG_UESP)
+                        ignore_reg = true;
+#else
+                if (i == REG_CSGSFS) {
+                        struct selectors *req_sels =
+                                (void *)&requested_regs[REG_CSGSFS];
+                        struct selectors *res_sels =
+                                (void *)&resulting_regs[REG_CSGSFS];
+                        if (req_sels->cs != res_sels->cs) {
+                                printf("[FAIL]\tCS mismatch: requested 0x%hx; got 0x%hx\n",
+                                       req_sels->cs, res_sels->cs);
+                                nerrs++;
+                        }
+
+                        if (req_sels->ss != res_sels->ss) {
+                                printf("[FAIL]\tSS mismatch: requested 0x%hx; got 0x%hx\n",
+                                       req_sels->ss, res_sels->ss);
+                                nerrs++;
+                        }
+
+                        continue;
+                }
+#endif
+
+                /* Sanity check on the kernel */
+                if (i == REG_AX && requested_regs[i] != resulting_regs[i]) {
+                        printf("[FAIL]\tAX (saved SP) mismatch: requested 0x%llx; got 0x%llx\n",
+                               (unsigned long long)requested_regs[i],
+                               (unsigned long long)resulting_regs[i]);
+                        nerrs++;
+                        continue;
+                }
+
+                if (requested_regs[i] != resulting_regs[i] && !ignore_reg) {
+                        /*
+                         * SP is particularly interesting here.  The
+                         * usual cause of failures is that we hit the
+                         * nasty IRET case of returning to a 16-bit SS,
+                         * in which case bits 16:31 of the *kernel*
+                         * stack pointer persist in ESP.
+                         */
+                        printf("[FAIL]\tReg %d mismatch: requested 0x%llx; got 0x%llx\n",
+                               i, (unsigned long long)requested_regs[i],
+                               (unsigned long long)resulting_regs[i]);
+                        nerrs++;
+                }
+        }
+
+        if (nerrs == 0)
+                printf("[OK]\tall registers okay\n");
+
+        return nerrs;
+}
+
+static int test_bad_iret(int cs_bits, unsigned short ss, int force_cs)
+{
+        int cs = force_cs == -1 ? find_cs(cs_bits) : force_cs;
+        if (cs == -1)
+                return 0;
+
+        sig_cs = cs;
+        sig_ss = ss;
+
+        printf("[RUN]\t%d-bit CS (%hx), bogus SS (%hx)\n",
+               cs_bits, sig_cs, sig_ss);
+
+        sig_trapped = 0;
+        raise(SIGUSR1);
+        if (sig_trapped) {
+                char errdesc[32] = "";
+                if (sig_err) {
+                        const char *src = (sig_err & 1) ? " EXT" : "";
+                        const char *table;
+                        if ((sig_err & 0x6) == 0x0)
+                                table = "GDT";
+                        else if ((sig_err & 0x6) == 0x4)
+                                table = "LDT";
+                        else if ((sig_err & 0x6) == 0x2)
+                                table = "IDT";
+                        else
+                                table = "???";
+
+                        sprintf(errdesc, "%s%s index %d, ",
+                                table, src, sig_err >> 3);
+                }
+
+                char trapname[32];
+                if (sig_trapno == 13)
+                        strcpy(trapname, "GP");
+                else if (sig_trapno == 11)
+                        strcpy(trapname, "NP");
+                else if (sig_trapno == 12)
+                        strcpy(trapname, "SS");
+                else if (sig_trapno == 32)
+                        strcpy(trapname, "IRET");  /* X86_TRAP_IRET */
+                else
+                        sprintf(trapname, "%d", sig_trapno);
+
+                printf("[OK]\tGot #%s(0x%lx) (i.e. %s%s)\n",
+                       trapname, (unsigned long)sig_err,
+                       errdesc, strsignal(sig_trapped));
+                return 0;
+        } else {
+                printf("[FAIL]\tDid not get SIGSEGV\n");
+                return 1;
+        }
+}
+
+int main()
+{
+        int total_nerrs = 0;
+        unsigned short my_cs, my_ss;
+
+        asm volatile ("mov %%cs,%0" : "=r" (my_cs));
+        asm volatile ("mov %%ss,%0" : "=r" (my_ss));
+        setup_ldt();
+
+        stack_t stack = {
+                .ss_sp = altstack_data,
+                .ss_size = SIGSTKSZ,
+        };
+        if (sigaltstack(&stack, NULL) != 0)
+                err(1, "sigaltstack");
+
+        sethandler(SIGUSR1, sigusr1, 0);
+        sethandler(SIGTRAP, sigtrap, SA_ONSTACK);
+
+        /* Easy cases: return to a 32-bit SS in each possible CS bitness. */
+        total_nerrs += test_valid_sigreturn(64, false, -1);
+        total_nerrs += test_valid_sigreturn(32, false, -1);
+        total_nerrs += test_valid_sigreturn(16, false, -1);
+
+        /*
+         * Test easy espfix cases: return to a 16-bit LDT SS in each possible
+         * CS bitness.  NB: with a long mode CS, the SS bitness is irrelevant.
+         *
+         * This catches the original missing-espfix-on-64-bit-kernels issue
+         * as well as CVE-2014-8134.
+         */
+        total_nerrs += test_valid_sigreturn(64, true, -1);
+        total_nerrs += test_valid_sigreturn(32, true, -1);
+        total_nerrs += test_valid_sigreturn(16, true, -1);
+
+        if (gdt_data16_idx) {
+                /*
+                 * For performance reasons, Linux skips espfix if SS points
+                 * to the GDT.  If we were able to allocate a 16-bit SS in
+                 * the GDT, see if it leaks parts of the kernel stack pointer.
+                 *
+                 * This tests for CVE-2014-8133.
+                 */
+                total_nerrs += test_valid_sigreturn(64, true,
+                                                    GDT3(gdt_data16_idx));
+                total_nerrs += test_valid_sigreturn(32, true,
+                                                    GDT3(gdt_data16_idx));
+                total_nerrs += test_valid_sigreturn(16, true,
+                                                    GDT3(gdt_data16_idx));
+        }
+
+        /*
+         * We're done testing valid sigreturn cases.  Now we test states
+         * for which sigreturn itself will succeed but the subsequent
+         * entry to user mode will fail.
+         *
+         * Depending on the failure mode and the kernel bitness, these
+         * entry failures can generate SIGSEGV, SIGBUS, or SIGILL.
+         */
+        clearhandler(SIGTRAP);
+        sethandler(SIGSEGV, sigtrap, SA_ONSTACK);
+        sethandler(SIGBUS, sigtrap, SA_ONSTACK);
+        sethandler(SIGILL, sigtrap, SA_ONSTACK);  /* 32-bit kernels do this */
+
+        /* Easy failures: invalid SS, resulting in #GP(0) */
+        test_bad_iret(64, ldt_nonexistent_sel, -1);
+        test_bad_iret(32, ldt_nonexistent_sel, -1);
+        test_bad_iret(16, ldt_nonexistent_sel, -1);
+
+        /* These fail because SS isn't a data segment, resulting in #GP(SS) */
+        test_bad_iret(64, my_cs, -1);
+        test_bad_iret(32, my_cs, -1);
+        test_bad_iret(16, my_cs, -1);
+
+        /* Try to return to a not-present code segment, triggering #NP(SS). */
+        test_bad_iret(32, my_ss, npcode32_sel);
+
+        /*
+         * Try to return to a not-present but otherwise valid data segment.
+         * This will cause IRET to fail with #SS on the espfix stack.  This
+         * exercises CVE-2014-9322.
+         *
+         * Note that, if espfix is enabled, 64-bit Linux will lose track
+         * of the actual cause of failure and report #GP(0) instead.
+         * This would be very difficult for Linux to avoid, because
+         * espfix64 causes IRET failures to be promoted to #DF, so the
+         * original exception frame is never pushed onto the stack.
+         */
+        test_bad_iret(32, npdata32_sel, -1);
+
+        /*
+         * Try to return to a not-present but otherwise valid data
+         * segment without invoking espfix.  Newer kernels don't allow
+         * this to happen in the first place.  On older kernels, though,
+         * this can trigger CVE-2014-9322.
+         */
+        if (gdt_npdata32_idx)
+                test_bad_iret(32, GDT3(gdt_npdata32_idx), -1);
+
+        return total_nerrs ? 1 : 0;
+}
diff --git a/tools/testing/selftests/x86/trivial_32bit_program.c b/tools/testing/selftests/x86/trivial_32bit_program.c
new file mode 100644
index 000000000000..2e231beb0a39
--- /dev/null
+++ b/tools/testing/selftests/x86/trivial_32bit_program.c
@@ -0,0 +1,14 @@
+/*
+ * Trivial program to check that we have a valid 32-bit build environment.
+ * Copyright (c) 2015 Andy Lutomirski
+ * GPL v2
+ */
+
+#include <stdio.h>
+
+int main()
+{
+        printf("\n");
+
+        return 0;
+}