FAILED: patch "[PATCH] x86/alternatives: Disable KASAN in apply_alternatives()" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x d35652a5fc9944784f6f50a5c979518ff8dacf61
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023101551-eardrum-control-9aae@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

d35652a5fc99 ("x86/alternatives: Disable KASAN in apply_alternatives()")
6becb5026b81 ("x86/alternative: Make debug-alternative selective")
ac0ee0a9560c ("x86/alternatives: Teach text_poke_bp() to patch Jcc.d32 instructions") 5d1dd961e743 ("x86/alternatives: Add alt_instr.flags")
931ab63664f0 ("x86/ibt: Implement FineIBT")
b341b20d648b ("x86: Add prefix symbols for function padding")
3b6c1747da48 ("x86/retpoline: Add SKL retthunk retpolines")
52354973573c ("x86/asm: Provide ALTERNATIVE_3")
eaf44c816ed8 ("x86/modules: Add call patching")
e81dc127ef69 ("x86/callthunks: Add call patching for call depth tracking")
80e4c1cd42ff ("x86/retbleed: Add X86_FEATURE_CALL_DEPTH")
bea75b33895f ("x86/Kconfig: Introduce function padding")
8f7c0d8b23c3 ("x86/Kconfig: Add CONFIG_CALL_THUNKS")
8eb5d34e77c6 ("x86/asm: Differentiate between code and function alignment")
d49a0626216b ("arch: Introduce CONFIG_FUNCTION_ALIGNMENT")
8afc66e8d43b ("Merge tag 'kbuild-v6.1' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d35652a5fc9944784f6f50a5c979518ff8dacf61 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <[email protected]>
Date: Thu, 12 Oct 2023 13:04:24 +0300
Subject: [PATCH] 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 ]

index 517ee01503be..73be3931e4f0 100644
@@ -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)

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 ]

---
 arch/x86/kernel/alternative.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

index e6e63a9d27cb..d58621f0fe51 100644
@@ -424,6 +424,17 @@ 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.

@@ -491,6 +502,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 next:
 		optimize_nops(instr, a->instrlen);
 	}
+
+	kasan_enable_current();
 }
 
 #if defined(CONFIG_RETPOLINE) && defined(CONFIG_STACK_VALIDATION)

2.41.0