[llvm-dev] [compiler-rt] Use of ESR context in AArch64 sigframe

[Dmitry Vyukov via llvm-dev]

On Wed, Mar 7, 2018 at 4:39 PM, Andrey Ryabinin <aryabinin at virtuozzo.com> wrote:
> On 03/06/2018 08:58 PM, Will Deacon wrote:
>> Hi all,
>>
>> As part of some recent work to harden the Kernel Address Space Layout
>> Randomisation (KASLR) implementation in arm64 Linux, I've proposed a
>> patch for the kernel which omits the ESR context from the signal frame
>> if the faulting virtual address is outside the range of addresses which
>> can be mapped by userspace.
>>
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2018-March/563837.html
>>
>> Looking around, it seems that AddressSanitizer is using this information
>> in compiler-rt in order to distinguish the faulting access type between
>> READ, WRITE or UNKNOWN. With this change, all attempted accesses to kernel
>> memory from userspace will be reported as UNKNOWN.
>>
>> Is this likely to cause a problem?
>
> I guess this shouldn't be a bid deal.
> AFAICS compiler-rt uses this information only in diagnostic message.

+address-sanitizer mailing list

Hi,

These diagnostic messages are then parsed and analyzed, and access
type is used at least during automatic security pre-assessment. Being
capable to read arbitrary memory is different from being able to write
arbitrary memory. Though, I don't know how we treat UNKNOWN. If it's
the same as WRITE, then it's probably fine.