diff options
| author | Andy Lutomirski <luto@kernel.org> | 2018-04-17 07:36:36 -0700 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2018-04-27 17:07:58 +0200 |
| commit | 8bb2610bc4967f19672444a7b0407367f1540028 (patch) | |
| tree | c0d0fec57aa9866fad60d843fa32f6b84d5c9ed8 /arch/x86/entry | |
| parent | 316d097c4cd4e7f2ef50c40cff2db266593c4ec4 (diff) | |
x86/entry/64/compat: Preserve r8-r11 in int $0x80
32-bit user code that uses int $80 doesn't care about r8-r11. There is,
however, some 64-bit user code that intentionally uses int $0x80 to invoke
32-bit system calls. From what I've seen, basically all such code assumes
that r8-r15 are all preserved, but the kernel clobbers r8-r11. Since I
doubt that there's any code that depends on int $0x80 zeroing r8-r11,
change the kernel to preserve them.
I suspect that very little user code is broken by the old clobber, since
r8-r11 are only rarely allocated by gcc, and they're clobbered by function
calls, so they only way we'd see a problem is if the same function that
invokes int $0x80 also spills something important to one of these
registers.
The current behavior seems to date back to the historical commit
"[PATCH] x86-64 merge for 2.6.4". Before that, all regs were
preserved. I can't find any explanation of why this change was made.
Update the test_syscall_vdso_32 testcase as well to verify the new
behavior, and it strengthens the test to make sure that the kernel doesn't
accidentally permute r8..r15.
Suggested-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Link: https://lkml.kernel.org/r/d4c4d9985fbe64f8c9e19291886453914b48caee.1523975710.git.luto@kernel.org
Diffstat (limited to 'arch/x86/entry')
| -rw-r--r-- | arch/x86/entry/entry_64_compat.S | 8 |
1 files changed, 4 insertions, 4 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 */ |