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

[Lucas De Marchi]

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)

Acked-by: Lucas De Marchi <lucas.demarchi at intel.com>

Lucas De Marchi