linux-kernel - [PATCH v5 7/7] x86/boot: Remove KASAN workaround for 4/5 level paging switch

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Message-ID: <20250520104138.2734372-16-ardb+git@google.com>
Date: Tue, 20 May 2025 12:41:46 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>, Ingo Molnar <mingo@...nel.org>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Brian Gerst <brgerst@...il.com>, 
	"Kirill A. Shutemov" <kirill@...temov.name>, Borislav Petkov <bp@...en8.de>
Subject: [PATCH v5 7/7] x86/boot: Remove KASAN workaround for 4/5 level paging switch

From: Ard Biesheuvel <ardb@...nel.org>

pgtable_l5_enabled() is no longer based on a CPU feature bit that might
change values and confuse KASAN, so we no longer need to disable it
temporarily.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/kernel/alternative.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index f3c68b586a95..e39823d8d1ae 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -589,16 +589,6 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 
 	DPRINTK(ALT, "alt table %px, -> %px", start, end);
 
-	/*
-	 * 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.
@@ -666,8 +656,6 @@ 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)
-- 
2.49.0.1101.gccaa498523-goog