On Tue, Feb 23 2021 at 10:15, Andy Lutomirski wrote:
> On a 32-bit fast syscall that fails to read its arguments from user
> memory, the kernel currently does syscall exit work but not
> syscall entry work. This confuses audit and ptrace. For example:
>
> $ ./tools/testing/selftests/x86/syscall_arg_fault_32
> ...
> strace: pid 264258: entering, ptrace_syscall_info.op == 2
> ...
>
> This is a minimal fix intended for ease of backporting. A more
> complete cleanup is coming.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 0b085e68f407 ("x86/entry: Consolidate 32/64 bit syscall entry")
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> ---
> arch/x86/entry/common.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index 0904f5676e4d..cf4dcf346ca8 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -128,7 +128,8 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
> regs->ax = -EFAULT;
>
> instrumentation_end();
> - syscall_exit_to_user_mode(regs);
> + local_irq_disable();
> + exit_to_user_mode();
That's still the same as the previous version. The right function (while
the name is misleading) to invoke here is irqentry_exit_to_user_mode()
because that invokes exit_to_user_mode_prepare() before
exit_to_user_mode(). We can rename that function afterwards.
Thanks,
tglx
