linux-kernel - [RFC PATCH 33/56] x86/alternative: Avoid re-patching init code

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Message-ID: <20251013143444.3999-34-david.kaplan@amd.com>
Date: Mon, 13 Oct 2025 09:34:21 -0500
From: David Kaplan <david.kaplan@....com>
To: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Ingo Molnar
	<mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>
CC: Alexander Graf <graf@...zon.com>, Boris Ostrovsky
	<boris.ostrovsky@...cle.com>, <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 33/56] x86/alternative: Avoid re-patching init code

During boot, all sites should be patched but during re-patch, ignore any
sites that are in the init section of the kernel or a module.

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 arch/x86/kernel/alternative.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 9fbec219e98e..a821ea37fc29 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -298,6 +298,27 @@ u8 *its_static_thunk(int reg)
 static inline void its_fini_core(void) {}
 #endif /* CONFIG_MITIGATION_ITS */
 
+static bool __maybe_unused repatch_in_progress;
+
+#ifdef CONFIG_DYNAMIC_MITIGATIONS
+/* Do not patch __init text addresses when repatching */
+static bool should_patch(void *addr, struct module *mod)
+{
+	if (!repatch_in_progress)
+		return true;
+
+	if (is_kernel_text((u64) addr))
+		return true;
+
+	return mod && within_module_core((u64) addr, mod);
+}
+#else
+static bool should_patch(void *addr, struct module *mod)
+{
+	return true;
+}
+#endif
+
 /*
  * Nomenclature for variable names to simplify and clarify this code and ease
  * any potential staring at it:
@@ -658,6 +679,10 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		}
 
 		instr = instr_va(a);
+
+		if (!should_patch(instr, mod))
+			continue;
+
 		replacement = (u8 *)&a->repl_offset + a->repl_offset;
 		BUG_ON(a->instrlen > sizeof(insn_buff));
 		BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32);
@@ -986,6 +1011,10 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end, struct mod
 		u8 *dest;
 
 		ret = insn_decode_kernel(&insn, addr);
+
+		if (!should_patch(addr, mod))
+			continue;
+
 		if (WARN_ON_ONCE(ret < 0))
 			continue;
 
@@ -1092,6 +1121,10 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end, struct module
 		u8 op;
 
 		ret = insn_decode_kernel(&insn, addr);
+
+		if (!should_patch(addr, mod))
+			continue;
+
 		if (WARN_ON_ONCE(ret < 0))
 			continue;
 
-- 
2.34.1