x86/alternatives: Disable KASAN in apply_alternatives()
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: 6657fca06e
("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
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@ -403,6 +403,17 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
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u8 insn_buff[MAX_PATCH_LEN];
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DPRINTK(ALT, "alt table %px, -> %px", start, end);
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/*
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* In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using
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* cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here.
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* During the process, KASAN becomes confused seeing partial LA57
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* conversion and triggers a false-positive out-of-bound report.
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*
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* Disable KASAN until the patching is complete.
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*/
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kasan_disable_current();
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/*
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* The scan order should be from start to end. A later scanned
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* alternative code can overwrite previously scanned alternative code.
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@ -452,6 +463,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
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text_poke_early(instr, insn_buff, insn_buff_sz);
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}
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kasan_enable_current();
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}
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static inline bool is_jcc32(struct insn *insn)
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