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

From: Dmitry Safonov
Date: Fri Feb 10 2017 - 07:02:43 EST

On 02/10/2017 02:52 PM, Dmitry Safonov wrote:
Kernel erases R8..R11 registers prior returning to userspace
from int80:

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:

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(-)