Re: [PATCH 6.1.y] x86/alternatives: Disable KASAN in apply_alternatives()

[Greg KH <greg@kroah.com>]

On Sun, Oct 15, 2023 at 11:09:08PM +0300, Kirill A. Shutemov wrote:
> 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@intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: stable@vger.kernel.org
> Link: https://lore.kernel.org/r/20231012100424.1456-1-kirill.shutemov@linux.intel.com
> (cherry picked from commit d35652a5fc9944784f6f50a5c979518ff8dacf61)
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  arch/x86/kernel/alternative.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)

All now queued up, thanks.

greg k-h