x86/debug: Implement __WARN() using UD0

By using "UD0" for WARN()s we remove the function call and its possible
__FILE__ and __LINE__ immediate arguments from the instruction stream.

Total image size will not change much, what we win in the instruction
stream we'll lose because of the __bug_table entries. Still, saves on
I$ footprint and the total image size does go down a bit.

      text    data       filename
  10702123    4530992    defconfig-build/vmlinux.orig
  10682460    4530992    defconfig-build/vmlinux.patched

(UML didn't seem to use GENERIC_BUG at all, so remove it)

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

8 files changed, 101 insertions, 76 deletions

diff --git a/arch/um/Kconfig.common b/arch/um/Kconfig.common
index fd443852103c..ed9c5b5ff028 100644
--- a/arch/um/Kconfig.common
+++ b/arch/um/Kconfig.common
@@ -50,11 +50,6 @@ config GENERIC_CALIBRATE_DELAY
         bool
         default y
 
-config GENERIC_BUG
-        bool
-        default y
-        depends on BUG
-
 config HZ
         int
         default 100
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index ba38ebbaced3..4fde330c44b7 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -1,36 +1,78 @@
 #ifndef _ASM_X86_BUG_H
 #define _ASM_X86_BUG_H
 
-#define HAVE_ARCH_BUG
+#include <linux/stringify.h>
 
-#ifdef CONFIG_DEBUG_BUGVERBOSE
+/*
+ * Since some emulators terminate on UD2, we cannot use it for WARN.
+ * Since various instruction decoders disagree on the length of UD1,
+ * we cannot use it either. So use UD0 for WARN.
+ *
+ * (binutils knows about "ud1" but {en,de}codes it as 2 bytes, whereas
+ *  our kernel decoder thinks it takes a ModRM byte, which seems consistent
+ *  with various things like the Intel SDM instruction encoding rules)
+ */
+
+#define ASM_UD0         ".byte 0x0f, 0xff"
+#define ASM_UD1         ".byte 0x0f, 0xb9" /* + ModRM */
+#define ASM_UD2         ".byte 0x0f, 0x0b"
+
+#define INSN_UD0        0xff0f
+#define INSN_UD2        0x0b0f
+
+#define LEN_UD0         2
+
+#ifdef CONFIG_GENERIC_BUG
+#define HAVE_ARCH_BUG
 
 #ifdef CONFIG_X86_32
-# define __BUG_C0       "2:\t.long 1b, %c0\n"
+# define __BUG_REL(val) ".long " __stringify(val)
 #else
-# define __BUG_C0       "2:\t.long 1b - 2b, %c0 - 2b\n"
+# define __BUG_REL(val) ".long " __stringify(val) " - 2b"
 #endif
 
-#define BUG()                                                   \
-do {                                                            \
-        asm volatile("1:\tud2\n"                                \
-                     ".pushsection __bug_table,\"a\"\n"         \
-                     __BUG_C0                                   \
-                     "\t.word %c1, 0\n"                         \
-                     "\t.org 2b+%c2\n"                          \
-                     ".popsection"                              \
-                     : : "i" (__FILE__), "i" (__LINE__),        \
-                     "i" (sizeof(struct bug_entry)));           \
-        unreachable();                                          \
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+
+#define _BUG_FLAGS(ins, flags)                                          \
+do {                                                                    \
+        asm volatile("1:\t" ins "\n"                                    \
+                     ".pushsection __bug_table,\"a\"\n"                 \
+                     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"   \
+                     "\t"  __BUG_REL(%c0) "\t# bug_entry::file\n"       \
+                     "\t.word %c1"        "\t# bug_entry::line\n"       \
+                     "\t.word %c2"        "\t# bug_entry::flags\n"      \
+                     "\t.org 2b+%c3\n"                                  \
+                     ".popsection"                                      \
+                     : : "i" (__FILE__), "i" (__LINE__),                \
+                         "i" (flags),                                   \
+                         "i" (sizeof(struct bug_entry)));               \
 } while (0)
 
-#else
+#else /* !CONFIG_DEBUG_BUGVERBOSE */
+
+#define _BUG_FLAGS(ins, flags)                                          \
+do {                                                                    \
+        asm volatile("1:\t" ins "\n"                                    \
+                     ".pushsection __bug_table,\"a\"\n"                 \
+                     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"   \
+                     "\t.word %c0"        "\t# bug_entry::flags\n"      \
+                     "\t.org 2b+%c1\n"                                  \
+                     ".popsection"                                      \
+                     : : "i" (flags),                                   \
+                         "i" (sizeof(struct bug_entry)));               \
+} while (0)
+
+#endif /* CONFIG_DEBUG_BUGVERBOSE */
+
 #define BUG()                                                   \
 do {                                                            \
-        asm volatile("ud2");                                    \
+        _BUG_FLAGS(ASM_UD2, 0);                                 \
         unreachable();                                          \
 } while (0)
-#endif
+
+#define __WARN_TAINT(taint)     _BUG_FLAGS(ASM_UD0, BUGFLAG_TAINT(taint))
+
+#endif /* CONFIG_GENERIC_BUG */
 
 #include <asm-generic/bug.h>
 
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 09d4ac0d2661..924f45ea4382 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -289,9 +289,6 @@ void die(const char *str, struct pt_regs *regs, long err)
         unsigned long flags = oops_begin();
         int sig = SIGSEGV;
 
-        if (!user_mode(regs))
-                report_bug(regs->ip, regs);
-
         if (__die(str, regs, err))
                 sig = 0;
         oops_end(flags, regs, sig);
diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index b0b3a3df7c20..e5f0b40e66d2 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -162,15 +162,3 @@ void show_regs(struct pt_regs *regs)
         }
         pr_cont("\n");
 }
-
-int is_valid_bugaddr(unsigned long ip)
-{
-        unsigned short ud2;
-
-        if (ip < PAGE_OFFSET)
-                return 0;
-        if (probe_kernel_address((unsigned short *)ip, ud2))
-                return 0;
-
-        return ud2 == 0x0b0f;
-}
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index a8b117e93b46..3e1471d57487 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -178,13 +178,3 @@ void show_regs(struct pt_regs *regs)
         }
         pr_cont("\n");
 }
-
-int is_valid_bugaddr(unsigned long ip)
-{
-        unsigned short ud2;
-
-        if (__copy_from_user(&ud2, (const void __user *) ip, sizeof(ud2)))
-                return 0;
-
-        return ud2 == 0x0b0f;
-}
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 948443e115c1..3c0751b120de 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -169,6 +169,37 @@ void ist_end_non_atomic(void)
         preempt_disable();
 }
 
+int is_valid_bugaddr(unsigned long addr)
+{
+        unsigned short ud;
+
+        if (addr < TASK_SIZE_MAX)
+                return 0;
+
+        if (probe_kernel_address((unsigned short *)addr, ud))
+                return 0;
+
+        return ud == INSN_UD0 || ud == INSN_UD2;
+}
+
+static int fixup_bug(struct pt_regs *regs, int trapnr)
+{
+        if (trapnr != X86_TRAP_UD)
+                return 0;
+
+        switch (report_bug(regs->ip, regs)) {
+        case BUG_TRAP_TYPE_NONE:
+        case BUG_TRAP_TYPE_BUG:
+                break;
+
+        case BUG_TRAP_TYPE_WARN:
+                regs->ip += LEN_UD0;
+                return 1;
+        }
+
+        return 0;
+}
+
 static nokprobe_inline int
 do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
                   struct pt_regs *regs, long error_code)
@@ -187,12 +218,15 @@ do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
         }
 
         if (!user_mode(regs)) {
-                if (!fixup_exception(regs, trapnr)) {
-                        tsk->thread.error_code = error_code;
-                        tsk->thread.trap_nr = trapnr;
-                        die(str, regs, error_code);
-                }
-                return 0;
+                if (fixup_exception(regs, trapnr))
+                        return 0;
+
+                if (fixup_bug(regs, trapnr))
+                        return 0;
+
+                tsk->thread.error_code = error_code;
+                tsk->thread.trap_nr = trapnr;
+                die(str, regs, error_code);
         }
 
         return -1;
diff --git a/arch/x86/um/Makefile b/arch/x86/um/Makefile
index e7e7055a8658..76f17f05446f 100644
--- a/arch/x86/um/Makefile
+++ b/arch/x86/um/Makefile
@@ -8,7 +8,7 @@ else
         BITS := 64
 endif
 
-obj-y = bug.o bugs_$(BITS).o delay.o fault.o ldt.o \
+obj-y = bugs_$(BITS).o delay.o fault.o ldt.o \
         ptrace_$(BITS).o ptrace_user.o setjmp_$(BITS).o signal.o \
         stub_$(BITS).o stub_segv.o \
         sys_call_table_$(BITS).o sysrq_$(BITS).o tls_$(BITS).o \
diff --git a/arch/x86/um/bug.c b/arch/x86/um/bug.c
deleted file mode 100644
index e8034e363d83..000000000000
--- a/arch/x86/um/bug.c
+++ /dev/null
@@ -1,21 +0,0 @@
-/*
- * Copyright (C) 2006 Jeff Dike (jdike@addtoit.com)
- * Licensed under the GPL V2
- */
-
-#include <linux/uaccess.h>
-
-/*
- * Mostly copied from i386/x86_86 - eliminated the eip < PAGE_OFFSET because
- * that's not relevant in skas mode.
- */
-
-int is_valid_bugaddr(unsigned long eip)
-{
-        unsigned short ud2;
-
-        if (probe_kernel_address((unsigned short __user *)eip, ud2))
-                return 0;
-
-        return ud2 == 0x0b0f;
-}