Re: [PATCH] MIPS: scall64-o32: Fix indirect syscall number load

[Philippe Mathieu-DaudÃ]

On 4/9/19 4:53 PM, Aurelien Jarno wrote:
> Commit 4c21b8fd8f14 (MIPS: seccomp: Handle indirect system calls (o32))
> added indirect syscall detection for O32 processes running on MIPS64,
> but it did not work correctly for big endian kernel/processes. The
> reason is that the syscall number is loaded from ARG1 using the lw
> instruction while this is a 64-bit value, so zero is loaded instead of
> the syscall number.
> 
> Fix the code by using the ld instruction instead. When running a 32-bit
> processes on a 64 bit CPU, the values are properly sign-extended, so it
> ensures the value passed to syscall_trace_enter is correct.
> 
> Recent systemd versions with seccomp enabled whitelist the getpid
> syscall for their internal  processes (e.g. systemd-journald), but call
> it through syscall(SYS_getpid). This fix therefore allows O32 big endian
> systems with a 64-bit kernel to run recent systemd versions.
> 
> Signed-off-by: Aurelien Jarno <aurelien@xxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v3.15+
> ---
>  arch/mips/kernel/scall64-o32.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/kernel/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
> index f158c5894a9a..feb2653490df 100644
> --- a/arch/mips/kernel/scall64-o32.S
> +++ b/arch/mips/kernel/scall64-o32.S
> @@ -125,7 +125,7 @@ trace_a_syscall:
>  	subu	t1, v0,  __NR_O32_Linux
>  	move	a1, v0
>  	bnez	t1, 1f /* __NR_syscall at offset 0 */
> -	lw	a1, PT_R4(sp) /* Arg1 for __NR_syscall case */
> +	ld	a1, PT_R4(sp) /* Arg1 for __NR_syscall case */
>  	.set	pop
>  
>  1:	jal	syscall_trace_enter
> 
> 

Reviewed-by: Philippe Mathieu-Daudà <f4bug@xxxxxxxxx>