On Wed, Oct 11, 2023 at 09:58:49AM +0300, Kirill A. Shutemov wrote:
Fei has reported that KASAN triggers during apply_alternatives() on 5-level paging machine:
Urgh @ KASAN splat, can't we summarize that?
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
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..b4cc4d7c0825 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 and triggers
because of partial LA57 convertion ..
* 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();
}
Other than that, ACK.