linux-kernel - [PATCH v2 4/5] powerpc/feature-fixups: Do not patch init section after init

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Message-Id: <8e9311fc1b057e4e6a2a3a0701ebcc74b787affe.1669969781.git.christophe.leroy@csgroup.eu>
Date:   Fri,  2 Dec 2022 09:31:42 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>, bgray@...ux.ibm.com
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2 4/5] powerpc/feature-fixups: Do not patch init section after init

Once init section is freed, attempting to patch init code
ends up in the weed.

Commit 51c3c62b58b3 ("powerpc: Avoid code patching freed init sections")
protected patch_instruction() against that, but it is the responsibility
of the caller to ensure that the patched memory is valid.

In the same spirit as jump_label with its jump_label_can_update()
function, add is_fixup_addr_valid() function to skip patching on
freed init section.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/lib/feature-fixups.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index 25168a59d1ce..80def1c2afcb 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -118,6 +118,12 @@ void do_feature_fixups(unsigned long value, void *fixup_start, void *fixup_end)
 }
 
 #ifdef CONFIG_PPC_BARRIER_NOSPEC
+static bool is_fixup_addr_valid(void *dest, size_t size)
+{
+	return system_state < SYSTEM_FREEING_INITMEM ||
+	       !init_section_contains(dest, size);
+}
+
 static int do_patch_fixups(long *start, long *end, unsigned int *instrs, int num)
 {
 	int i;
@@ -126,6 +132,9 @@ static int do_patch_fixups(long *start, long *end, unsigned int *instrs, int num
 		int j;
 		unsigned int *dest = (void *)start + *start;
 
+		if (!is_fixup_addr_valid(dest, sizeof(*instrs) * num))
+			continue;
+
 		pr_devel("patching dest %lx\n", (unsigned long)dest);
 
 		for (j = 0; j < num; j++)
@@ -144,6 +153,9 @@ static int do_patch_entry_fixups(long *start, long *end, unsigned int *instrs,
 	for (i = 0; start < end; start++, i++) {
 		unsigned int *dest = (void *)start + *start;
 
+		if (!is_fixup_addr_valid(dest, sizeof(*instrs) * 3))
+			continue;
+
 		pr_devel("patching dest %lx\n", (unsigned long)dest);
 
 		// See comment in do_entry_flush_fixups() RE order of patching
-- 
2.38.1