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    Subject[PATCH 4.4 041/266] powerpc/64: Use barrier_nospec in syscall entry
    Date
    From: Michael Ellerman <mpe@ellerman.id.au>

    commit 51973a815c6b46d7b23b68d6af371ad1c9d503ca upstream.

    Our syscall entry is done in assembly so patch in an explicit
    barrier_nospec.

    Based on a patch by Michal Suchanek.

    Signed-off-by: Michal Suchanek <msuchanek@suse.de>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/powerpc/kernel/entry_64.S | 10 ++++++++++
    1 file changed, 10 insertions(+)

    --- a/arch/powerpc/kernel/entry_64.S
    +++ b/arch/powerpc/kernel/entry_64.S
    @@ -36,6 +36,7 @@
    #include <asm/hw_irq.h>
    #include <asm/context_tracking.h>
    #include <asm/tm.h>
    +#include <asm/barrier.h>
    #ifdef CONFIG_PPC_BOOK3S
    #include <asm/exception-64s.h>
    #else
    @@ -177,6 +178,15 @@ system_call: /* label this so stack tr
    clrldi r8,r8,32
    15:
    slwi r0,r0,4
    +
    + barrier_nospec_asm
    + /*
    + * Prevent the load of the handler below (based on the user-passed
    + * system call number) being speculatively executed until the test
    + * against NR_syscalls and branch to .Lsyscall_enosys above has
    + * committed.
    + */
    +
    ldx r12,r11,r0 /* Fetch system call handler [ptr] */
    mtctr r12
    bctrl /* Call handler */

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