Re: [Qemu-arm] [Qemu-devel] [PATCH for-2.12 4/4] target/arm: Always set FAR to a known unknown value for debug exceptions

[Peter Maydell]

On 21 March 2018 at 22:29, Philippe Mathieu-Daudé <address@hidden> wrote:
> On 03/20/2018 02:41 PM, Peter Maydell wrote:
>> For debug exceptions due to breakpoints or the BKPT instruction which
>> are taken to AArch32, the Fault Address Register is architecturally
>> UNKNOWN.  We were using that as license to simply not set
>> env->exception.vaddress, but this isn't correct, because it will
>> expose to the guest whatever old value was in that field when
>> arm_cpu_do_interrupt_aarch32() writes it to the guest IFSR.  That old
>> value might be a FAR for a previous guest EL2 or secure exception, in
>> which case we shouldn't show it to an EL1 or non-secure exception
>> handler. It might also be a non-deterministic value, which is bad
>> for record-and-replay.
>>
>> Clear env->exception.vaddress before taking breakpoint debug
>> exceptions, to avoid this minor information leak.
>
> So this series is worth Cc'ing qemu-stable...?

I don't think so. This isn't a regression -- we've behaved this
way ever since we introduced LPAE support, five years or so ago.
In particular Linux doesn't care about it.

thanks
-- PMM