[Intel-xe] [PATCH 1/1] x86/alternatives: Disable KASAN in apply_alternatives()

[Yang, Fei]

> On Mon, Oct 16, 2023 at 08:40:24AM -0700, fei.yang at intel.com wrote:
>> From: "Kirill A. Shutemov" <kirill.shutemov at linux.intel.com>
>>
>> Fei has reported that KASAN triggers during apply_alternatives() on a
>> 5-level paging machine:
>>
>>      BUG: KASAN: out-of-bounds in rcu_is_watching()
>>      Read of size 4 at addr ff110003ee6419a0 by task swapper/0/0
>>      ...
>>      __asan_load4()
>>      rcu_is_watching()
>>      trace_hardirqs_on()
>>      text_poke_early()
>>      apply_alternatives()
>>      ...
>>
>> On machines with 5-level paging, cpu_feature_enabled(X86_FEATURE_LA57)
>> gets patched. It includes KASAN code, where KASAN_SHADOW_START depends
>> on __VIRTUAL_MASK_SHIFT, which is defined with cpu_feature_enabled().
>>
>> KASAN gets confused when apply_alternatives() patches the
>> KASAN_SHADOW_START users. A test patch that makes KASAN_SHADOW_START
>> static, by replacing __VIRTUAL_MASK_SHIFT with 56, works around the issue.
>>
>> Fix it for real by disabling KASAN while the kernel is patching alternatives.
>>
>> [ mingo: updated the changelog ]
>>
>> Fixes: 6657fca06e3f ("x86/mm: Allow to boot without LA57 if
>> CONFIG_X86_5LEVEL=y")
>> Reported-by: Fei Yang <fei.yang at intel.com>
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov at linux.intel.com>
>> Signed-off-by: Ingo Molnar <mingo at kernel.org>
>> Acked-by: Peter Zijlstra (Intel) <peterz at infradead.org>
>> Cc: Linus Torvalds <torvalds at linux-foundation.org>
>> Cc: stable at vger.kernel.org
>> Link:
>> https://lore.kernel.org/r/20231012100424.1456-1-kirill.shutemov@linux.
>> intel.com (cherry picked from commit
>> d35652a5fc9944784f6f50a5c979518ff8dacf61)
>> ---
>>  arch/x86/kernel/alternative.c | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>
> What stable tree(s) is this for?

Sorry for the noise, forgot to remove the Cc's. This is for our graphics CI.

> thanks,
>
> greg k-h
>