Re: [PATCH] x86/entry/64/compat: Fix "x86/entry/64/compat: Preserve r8-r11 in int $0x80"

Li Zhijian
2018-06-27T08:51:16Z

On 6/27/2018 1:45 PM, Andy Lutomirski wrote:
> Commit 8bb2610bc496 ("x86/entry/64/compat: Preserve r8-r11 in int
> $0x80") was busted. My original patch had a minor conflict with
> some of the nospec changes. git apply is very clever and silently
> accepted the patch by making the same changes to a different
> function in the same file. There was obviously a huge offset, but
> git apply for some reason doesn't feel any need to say so.
>
> Move the changes to the correct function. Now the
> test_syscall_vdso_32 selftests passes.
>
> If anyone cares to observe the original problem, try applying the
> patch at
> https://lore.kernel.org/lkml/d4c4d9985fbe64f8c9e19291886453914b48caee.1523975710.git.luto@kernel.org/raw
> to the kernel at 316d097c4cd4e7f2ef50c40cff2db266593c4ec4. git am and
> git apply accept the patch without any complaints at all. patch -p1
> at least prints out a message about the huge offset.
>
> Reported-by: zhijianx.li@intel.com
> Fixes: 8bb2610bc496 ("x86/entry/64/compat: Preserve r8-r11 in int $0x80")
> Cc: stable@vger.kernel.org
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Tested-by: Li Zhijian <zhijianx.li@intel.com>

> ---
> arch/x86/entry/entry_64_compat.S | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> index 9de7f1e1dede..7d0df78db727 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 %r8 /* pt_regs->r8 */
> + pushq $0 /* pt_regs->r8 = 0 */
> xorl %r8d, %r8d /* nospec r8 */
> - pushq %r9 /* pt_regs->r9 */
> + pushq $0 /* pt_regs->r9 = 0 */
> xorl %r9d, %r9d /* nospec r9 */
> - pushq %r10 /* pt_regs->r10 */
> + pushq $0 /* pt_regs->r10 = 0 */
> xorl %r10d, %r10d /* nospec r10 */
> - pushq %r11 /* pt_regs->r11 */
> + pushq $0 /* pt_regs->r11 = 0 */
> xorl %r11d, %r11d /* nospec r11 */
> pushq %rbx /* pt_regs->rbx */
> xorl %ebx, %ebx /* nospec rbx */
> @@ -374,13 +374,13 @@ ENTRY(entry_INT80_compat)
> pushq %rcx /* pt_regs->cx */
> xorl %ecx, %ecx /* nospec 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 */