On Mon, Jan 23, 2017 at 05:19:34PM +0000, Mark Rutland wrote:
> commit 7d9e8f71b989230bc613d121ca38507d34ada849 upstream.
>
> Generally, taking an unexpected exception should be a fatal event, and
> bad_mode is intended to cater for this. However, it should be possible
> to contain unexpected synchronous exceptions from EL0 without bringing
> the kernel down, by sending a SIGILL to the task.
>
> We tried to apply this approach in commit 9955ac47f4ba1c95 ("arm64:
> don't kill the kernel on a bad esr from el0"), by sending a signal for
> any bad_mode call resulting from an EL0 exception.
>
> However, this also applies to other unexpected exceptions, such as
> SError and FIQ. The entry paths for these exceptions branch to bad_mode
> without configuring the link register, and have no kernel_exit. Thus, if
> we take one of these exceptions from EL0, bad_mode will eventually
> return to the original user link register value.
>
> This patch fixes this by introducing a new bad_el0_sync handler to cater
> for the recoverable case, and restoring bad_mode to its original state,
> whereby it calls panic() and never returns. The recoverable case
> branches to bad_el0_sync with a bl, and returns to userspace via the
> usual ret_to_user mechanism.
>
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Fixes: 9955ac47f4ba1c95 ("arm64: don't kill the kernel on a bad esr from el0")
> Reported-by: Mark Salter <msalter@xxxxxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> ---
> arch/arm64/kernel/entry.S | 4 ++--
> arch/arm64/kernel/traps.c | 28 ++++++++++++++++++++++++----
> 2 files changed, 26 insertions(+), 6 deletions(-)
Thanks for this patch, now queued up.
greg k-h