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x86/alternatives: Disable KASAN in apply_alternatives()

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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
This commit is contained in:
Kirill A. Shutemov 2023-10-12 13:04:24 +03:00 committed by Ingo Molnar
parent f454b18e07
commit d35652a5fc
1 changed files with 13 additions and 0 deletions
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13
arch/x86/kernel/alternative.c
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@ -403,6 +403,17 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
u8 insn_buff[MAX_PATCH_LEN];
DPRINTK(ALT, "alt table %px, -> %px", start, end);
/*
* In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using
* cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here.
* During the process, KASAN becomes confused seeing partial LA57
* conversion and triggers a false-positive out-of-bound report.
*
* Disable KASAN until the patching is complete.
*/
kasan_disable_current();
/*
* The scan order should be from start to end. A later scanned
* alternative code can overwrite previously scanned alternative code.
@ -452,6 +463,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
text_poke_early(instr, insn_buff, insn_buff_sz);
}
kasan_enable_current();
}
static inline bool is_jcc32(struct insn *insn)