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SubjectRe: [PATCH RFC rebase 3/9] powerpc/64: Use barrier_nospec in syscall entry
On Thu, 15 Mar 2018 20:15:52 +0100
Michal Suchanek <msuchanek@suse.de> wrote:

> On powerpc syscall entry is done in assembly so patch in an explicit
> barrier_nospec.

Same comment as Linus for this -- the barriers are before the branch here,
so is it possible the branch instruction can be speculative while the index
is used to load the syscall table?

Thanks,
Nick

>
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> ---
> arch/powerpc/kernel/entry_64.S | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 2cb5109a7ea3..7bfc4cf48af2 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -36,6 +36,7 @@
> #include <asm/context_tracking.h>
> #include <asm/tm.h>
> #include <asm/ppc-opcode.h>
> +#include <asm/barrier.h>
> #include <asm/export.h>
> #ifdef CONFIG_PPC_BOOK3S
> #include <asm/exception-64s.h>
> @@ -159,6 +160,7 @@ system_call: /* label this so stack traces look sane */
> andi. r11,r10,_TIF_SYSCALL_DOTRACE
> bne .Lsyscall_dotrace /* does not return */
> cmpldi 0,r0,NR_syscalls
> + barrier_nospec
> bge- .Lsyscall_enosys
>
> .Lsyscall:
> @@ -319,6 +321,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> ld r10,TI_FLAGS(r10)
>
> cmpldi r0,NR_syscalls
> + barrier_nospec
> blt+ .Lsyscall
>
> /* Return code is already in r3 thanks to do_syscall_trace_enter() */

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