1 files changed, 76 insertions, 2 deletions

diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index 3bbbb1a4fb52..781861cc5ee8 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -115,7 +115,81 @@ void perf_get_regs_user(struct perf_regs *regs_user,
                         struct pt_regs *regs,
                         struct pt_regs *regs_user_copy)
 {
-        regs_user->regs = task_pt_regs(current);
-        regs_user->abi = perf_reg_abi(current);
+        struct pt_regs *user_regs = task_pt_regs(current);
+
+        /*
+         * If we're in an NMI that interrupted task_pt_regs setup, then
+         * we can't sample user regs at all.  This check isn't really
+         * sufficient, though, as we could be in an NMI inside an interrupt
+         * that happened during task_pt_regs setup.
+         */
+        if (regs->sp > (unsigned long)&user_regs->r11 &&
+            regs->sp <= (unsigned long)(user_regs + 1)) {
+                regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE;
+                regs_user->regs = NULL;
+                return;
+        }
+
+        /*
+         * RIP, flags, and the argument registers are usually saved.
+         * orig_ax is probably okay, too.
+         */
+        regs_user_copy->ip = user_regs->ip;
+        regs_user_copy->cx = user_regs->cx;
+        regs_user_copy->dx = user_regs->dx;
+        regs_user_copy->si = user_regs->si;
+        regs_user_copy->di = user_regs->di;
+        regs_user_copy->r8 = user_regs->r8;
+        regs_user_copy->r9 = user_regs->r9;
+        regs_user_copy->r10 = user_regs->r10;
+        regs_user_copy->r11 = user_regs->r11;
+        regs_user_copy->orig_ax = user_regs->orig_ax;
+        regs_user_copy->flags = user_regs->flags;
+
+        /*
+         * Don't even try to report the "rest" regs.
+         */
+        regs_user_copy->bx = -1;
+        regs_user_copy->bp = -1;
+        regs_user_copy->r12 = -1;
+        regs_user_copy->r13 = -1;
+        regs_user_copy->r14 = -1;
+        regs_user_copy->r15 = -1;
+
+        /*
+         * For this to be at all useful, we need a reasonable guess for
+         * sp and the ABI.  Be careful: we're in NMI context, and we're
+         * considering current to be the current task, so we should
+         * be careful not to look at any other percpu variables that might
+         * change during context switches.
+         */
+        if (IS_ENABLED(CONFIG_IA32_EMULATION) &&
+            task_thread_info(current)->status & TS_COMPAT) {
+                /* Easy case: we're in a compat syscall. */
+                regs_user->abi = PERF_SAMPLE_REGS_ABI_32;
+                regs_user_copy->sp = user_regs->sp;
+                regs_user_copy->cs = user_regs->cs;
+                regs_user_copy->ss = user_regs->ss;
+        } else if (user_regs->orig_ax != -1) {
+                /*
+                 * We're probably in a 64-bit syscall.
+                 * Warning: this code is severely racy.  At least it's better
+                 * than just blindly copying user_regs.
+                 */
+                regs_user->abi = PERF_SAMPLE_REGS_ABI_64;
+                regs_user_copy->sp = this_cpu_read(old_rsp);
+                regs_user_copy->cs = __USER_CS;
+                regs_user_copy->ss = __USER_DS;
+                regs_user_copy->cx = -1;  /* usually contains garbage */
+        } else {
+                /* We're probably in an interrupt or exception. */
+                regs_user->abi = user_64bit_mode(user_regs) ?
+                        PERF_SAMPLE_REGS_ABI_64 : PERF_SAMPLE_REGS_ABI_32;
+                regs_user_copy->sp = user_regs->sp;
+                regs_user_copy->cs = user_regs->cs;
+                regs_user_copy->ss = user_regs->ss;
+        }
+
+        regs_user->regs = regs_user_copy;
 }
 #endif /* CONFIG_X86_32 */