2 files changed, 25 insertions, 18 deletions

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 9af927e59d49..9de7f1e1dede 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -84,13 +84,13 @@ ENTRY(entry_SYSENTER_compat)
         pushq   %rdx                    /* pt_regs->dx */
         pushq   %rcx                    /* pt_regs->cx */
         pushq   $-ENOSYS                /* pt_regs->ax */
-        pushq   $0                      /* pt_regs->r8  = 0 */
+        pushq   %r8                     /* pt_regs->r8 */
         xorl    %r8d, %r8d              /* nospec   r8 */
-        pushq   $0                      /* pt_regs->r9  = 0 */
+        pushq   %r9                     /* pt_regs->r9 */
         xorl    %r9d, %r9d              /* nospec   r9 */
-        pushq   $0                      /* pt_regs->r10 = 0 */
+        pushq   %r10                    /* pt_regs->r10 */
         xorl    %r10d, %r10d            /* nospec   r10 */
-        pushq   $0                      /* pt_regs->r11 = 0 */
+        pushq   %r11                    /* pt_regs->r11 */
         xorl    %r11d, %r11d            /* nospec   r11 */
         pushq   %rbx                    /* pt_regs->rbx */
         xorl    %ebx, %ebx              /* nospec   rbx */
diff --git a/tools/testing/selftests/x86/test_syscall_vdso.c b/tools/testing/selftests/x86/test_syscall_vdso.c
index 40370354d4c1..c9c3281077bc 100644
--- a/tools/testing/selftests/x86/test_syscall_vdso.c
+++ b/tools/testing/selftests/x86/test_syscall_vdso.c
@@ -100,12 +100,19 @@ asm (
         "       shl     $32, %r8\n"
         "       orq     $0x7f7f7f7f, %r8\n"
         "       movq    %r8, %r9\n"
-        "       movq    %r8, %r10\n"
-        "       movq    %r8, %r11\n"
-        "       movq    %r8, %r12\n"
-        "       movq    %r8, %r13\n"
-        "       movq    %r8, %r14\n"
-        "       movq    %r8, %r15\n"
+        "       incq    %r9\n"
+        "       movq    %r9, %r10\n"
+        "       incq    %r10\n"
+        "       movq    %r10, %r11\n"
+        "       incq    %r11\n"
+        "       movq    %r11, %r12\n"
+        "       incq    %r12\n"
+        "       movq    %r12, %r13\n"
+        "       incq    %r13\n"
+        "       movq    %r13, %r14\n"
+        "       incq    %r14\n"
+        "       movq    %r14, %r15\n"
+        "       incq    %r15\n"
         "       ret\n"
         "       .code32\n"
         "       .popsection\n"
@@ -128,12 +135,13 @@ int check_regs64(void)
         int err = 0;
         int num = 8;
         uint64_t *r64 = &regs64.r8;
+        uint64_t expected = 0x7f7f7f7f7f7f7f7fULL;
 
         if (!kernel_is_64bit)
                 return 0;
 
         do {
-                if (*r64 == 0x7f7f7f7f7f7f7f7fULL)
+                if (*r64 == expected++)
                         continue; /* register did not change */
                 if (syscall_addr != (long)&int80) {
                         /*
@@ -147,18 +155,17 @@ int check_regs64(void)
                                 continue;
                         }
                 } else {
-                        /* INT80 syscall entrypoint can be used by
+                        /*
+                         * INT80 syscall entrypoint can be used by
                          * 64-bit programs too, unlike SYSCALL/SYSENTER.
                          * Therefore it must preserve R12+
                          * (they are callee-saved registers in 64-bit C ABI).
                          *
-                         * This was probably historically not intended,
-                         * but R8..11 are clobbered (cleared to 0).
-                         * IOW: they are the only registers which aren't
-                         * preserved across INT80 syscall.
+                         * Starting in Linux 4.17 (and any kernel that
+                         * backports the change), R8..11 are preserved.
+                         * Historically (and probably unintentionally), they
+                         * were clobbered or zeroed.
                          */
-                        if (*r64 == 0 && num <= 11)
-                                continue;
                 }
                 printf("[FAIL]\tR%d has changed:%016llx\n", num, *r64);
                 err++;