Re: [Qemu-devel] [prefix=PATCH for-2.12?] linux-user: check that all of AArch64 SVE extended sigframe is writable

[Richard Henderson <richard.henderson@linaro.org>]

On 04/16/2018 05:19 AM, Peter Maydell wrote:
> In commit 8c5931de0ac7738809 we added support for SVE extended
> sigframe records.  These mean that the signal frame might now be
> larger than the size of the target_rt_sigframe record, so make sure
> we call lock_user on the entire frame size when we're creating it.
> (The code for restoring the signal frame already correctly handles
> the extended records by locking the 'extra' section separately to the
> main section.)
> 
> In particular, this fixes a bug even for non-SVE signal frames,
> because it extends the locked section to cover the
> target_rt_frame_record. Previously this was part of 'struct
> target_rt_sigframe', but in commit e1eecd1d9d4c1ade3 we pulled
> it out into its own struct, and so locking the target_rt_sigframe
> alone doesn't cover it. This bug would mean that we would fail
> to correctly handle the case where a signal was taken with
> SP pointing 16 bytes into an unwritable page, with the page
> immediately below it in memory being writable.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> The requirements to trigger the bug sound implausible, except
> that the stack page might be unwritable because we just
> executed some trampoline code from it, so perhaps not so
> unlikely as it first seems? Not sure whether to put into 2.12
> or not...
> ---
>  linux-user/signal.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Yes, let's just go ahead and fix this all properly now.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~