Re: [PATCH] s390: fix syscall_get_error for compat processes

[Heiko Carstens <heiko.carstens@de.ibm.com>]

On Tue, Jun 02, 2020 at 09:00:51PM +0300, Dmitry V. Levin wrote:
> If both the tracer and the tracee are compat processes, and gprs[2]
> is assigned a value by __poke_user_compat, then the higher 32 bits
> of gprs[2] are cleared, IS_ERR_VALUE() always returns false, and
> syscall_get_error() always returns 0.
> 
> Fix the implementation by sign-extending the value for compat processes
> the same way as x86 implementation does.
> 
> The bug was exposed to user space by commit 201766a20e30f ("ptrace: add
> PTRACE_GET_SYSCALL_INFO request") and detected by strace test suite.
> 
> This change fixes strace syscall tampering on s390.
> 
> Fixes: 753c4dd6a2fa2 ("[S390] ptrace changes")
> Cc: Elvira Khabirova <lineprinter@altlinux.org>
> Cc: stable@vger.kernel.org # v2.6.28+
> Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
> ---
>  arch/s390/include/asm/syscall.h | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)

Applied, thank you!