Fei has reported that KASAN triggers during apply_alternatives() on 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) got patched. It includes KASAN code, where KASAN_SHADOW_START depends on __VIRTUAL_MASK_SHIFT, which is defined with the 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, fixes the issue.
Disable KASAN while kernel patches alternatives.
Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reported-by: Fei Yang fei.yang@intel.com Fixes: 6657fca06e3f ("x86/mm: Allow to boot without LA57 if CONFIG_X86_5LEVEL=y") Cc: stable@vger.kernel.org --- v3: - Summarize KASAN splat; - Update comment in apply_alternatives();
v2: - Move kasan_disable/_enable_current() to cover whole loop, not only text_poke_early(); - Adjust commit message. --- arch/x86/kernel/alternative.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 517ee01503be..73be3931e4f0 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -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)