Re: [PATCH 0/2] Support HWASAN with Intel LAM

["Martin Liška" <mliska@suse.cz>]

On 11/29/22 03:37, Hongtao Liu wrote:
> On Mon, Nov 28, 2022 at 10:40 PM Martin Liška <mliska@suse.cz> wrote:
>>
>> On 11/11/22 02:26, liuhongt via Gcc-patches wrote:
>>>    2 years ago, ARM folks support HWASAN[1] in GCC[2], and introduced several
>>> target hooks(Many thanks to their work) so other backends can do similar
>>> things if they have similar feature.
>>>    Intel LAM(linear Address Masking)[3 Charpter 14] supports similar feature with
>>> the upper bits of pointers can be used as metadata, LAM support two modes:
>>>    LAM_U48:bits 48-62 can be used as metadata
>>>    LAM_U57:bits 57-62 can be used as metedata.
>>>
>>> These 2 patches mainly support those target hooks, but HWASAN is not really
>>> enabled until the final decision for the LAM kernel interface which may take
>>> quite a long time. We have verified our patches with a "fake" interface locally[4], and
>>> decided to push the backend patches to the GCC13 to make other HWASAN developper's work
>>> easy.
>>
>> Hello.
>>
>> A few random comments I noticed:
>>
>> 1) please document the new target -mlam in extend.texi
> I will.

Thanks.

>> 2) the description speaks about bits [48-62] or [57-62], can explain why the patch contains:
>>
> Kernel will use bit 63 for special purposes, and here we want to
> extract the tag by shifting right the pointer 57 bits, and need to
> manually mask off bit63.

And thanks for the explanation.

Martin

>> +  /* Mask off bit63 when LAM_U57.  */
>> +  if (ix86_lam_type == lam_u57)
>> ?
>>
>> 3) Shouldn't the -lman option emit GNU_PROPERTY_X86_FEATURE_1_LAM_U57 or GNU_PROPERTY_X86_FEATURE_1_LAM_U48
>> .gnu.property note?
>>
>> 4) Can you please explain Florian's comment here:
>> https://gitlab.com/x86-psABIs/x86-64-ABI/-/merge_requests/13#note_1181396487
>>
>> Thanks,
>> Martin
>>
>>>
>>> [1] https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
>>> [2] https://gcc.gnu.org/pipermail/gcc-patches/2020-November/557857.html
>>> [3] https://www.intel.com/content/dam/develop/external/us/en/documents/architecture-instruction-set-extensions-programming-reference.pdf
>>> [4] https://gitlab.com/x86-gcc/gcc/-/tree/users/intel/lam/master
>>>
>>>
>>> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
>>> Ok for trunk?
>>>
>>> liuhongt (2):
>>>    Implement hwasan target_hook.
>>>    Enable hwasan for x86-64.
>>>
>>>   gcc/config/i386/i386-expand.cc  |  12 ++++
>>>   gcc/config/i386/i386-options.cc |   3 +
>>>   gcc/config/i386/i386-opts.h     |   6 ++
>>>   gcc/config/i386/i386-protos.h   |   2 +
>>>   gcc/config/i386/i386.cc         | 123 ++++++++++++++++++++++++++++++++
>>>   gcc/config/i386/i386.opt        |  16 +++++
>>>   libsanitizer/configure.tgt      |   1 +
>>>   7 files changed, 163 insertions(+)
>>>
>>
> 
>