From: Kirill A. Shutemov Date: Thu, 12 Oct 2023 10:04:24 +0000 (+0300) Subject: x86/alternatives: Disable KASAN in apply_alternatives() X-Git-Url: https://git.baikalelectronics.ru/sdk/?a=commitdiff_plain;h=5b784489c8158518bf7a466bb3cc045b0fb66b4b;p=kernel.git x86/alternatives: Disable KASAN in apply_alternatives() commit d35652a5fc9944784f6f50a5c979518ff8dacf61 upstream. 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 Signed-off-by: Kirill A. Shutemov Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20231012100424.1456-1-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index d1d92897ed6be..46b7ee0ab01a4 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -270,6 +270,17 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, u8 insn_buff[MAX_PATCH_LEN]; DPRINTK("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. @@ -337,6 +348,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, next: optimize_nops(instr, a->instrlen); } + + kasan_enable_current(); } static inline bool is_jcc32(struct insn *insn)