Re: [PATCH] x86/selftests: add clobbers for int80 on x86_64

[Dmitry Safonov]

On 02/10/2017 02:52 PM, Dmitry Safonov wrote:
> Kernel erases R8..R11 registers prior returning to userspace
> from int80: https://lkml.org/lkml/2009/10/1/164
>
> GCC can reuse this registers and doesn't expect them to change
> during syscall invocation. I met this kind of bug in CRIU once
> gcc 6.1 and clang stored local variables in those registers
> and the kernel zerofied them during syscall:
> https://github.com/xemul/criu/commit/990d33f1a1cdd17bca6c2eb059ab3be2564f7fa2
>
> By that reason I suggest to add those registers to clobbers
> in selftests.
>
> Cc: Shuah Khan <shuah@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: linux-kselftest@xxxxxxxxxxxxxxx
> Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
> ---
>  tools/testing/selftests/x86/fsgsbase.c            |  2 +-
>  tools/testing/selftests/x86/iopl.c                | 10 ++++++++--

Drop this one: iopl doesn't do int80 - it's my failure in grepping.
Will resend.

>  tools/testing/selftests/x86/ldt_gdt.c             | 16 +++++++++++-----
>  tools/testing/selftests/x86/ptrace_syscall.c      |  3 ++-
>  tools/testing/selftests/x86/single_step_syscall.c |  5 ++++-
>  5 files changed, 26 insertions(+), 10 deletions(-)

--
             Dmitry