[PATCH 1/3] powerpc/code-patching: work around code patching verification in patching tests

Code patching tests patch the stack and (non-module) vmalloc space now,
which falls afoul of the new address check.

The stack patching can easily be fixed, but the vmalloc patching is more
difficult. For now, add an ugly workaround to skip the check while the
test code is running.

Fixes: 8b8a8f0ab3f55 ("powerpc/code-patching: Improve verification of patchability")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/lib/code-patching.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 5e2fe133639e..57e160963ab7 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c

@@ -187,10 +187,12 @@ static int do_patch_instruction(u32 *addr, struct ppc_inst instr)
 
 #endif /* CONFIG_STRICT_KERNEL_RWX */
 
+static bool skip_addr_verif = false;
+
 int patch_instruction(u32 *addr, struct ppc_inst instr)
 {
 	/* Make sure we aren't patching a freed init section */
-	if (!kernel_text_address((unsigned long)addr))
+	if (!skip_addr_verif && !kernel_text_address((unsigned long)addr))
 		return 0;
 
 	return do_patch_instruction(addr, instr);

@@ -738,11 +740,13 @@ static int __init test_code_patching(void)
 {
 	printk(KERN_DEBUG "Running code patching self-tests ...\n");
 
+	skip_addr_verif = true;
 	test_branch_iform();
 	test_branch_bform();
 	test_create_function_call();
 	test_translate_branch();
 	test_prefixed_patching();
+	skip_addr_verif = false;
 
 	return 0;
 }

-- 
2.23.0

Callers are supposed to handle this, but it is possible that they
don't or they do but don't make much noise about it. A failure is
probably an indication of a bigger problem somewhere so it is good
to warn once about it.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/lib/code-patching.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 57e160963ab7..70247fc58b6e 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c

@@ -161,6 +161,7 @@ static int do_patch_instruction(u32 *addr, struct ppc_inst instr)
 
 	text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr;
 	if (map_patch_area(addr, text_poke_addr)) {
+		WARN_ON_ONCE(1);
 		err = -1;
 		goto out;
 	}

@@ -192,8 +193,10 @@ static bool skip_addr_verif = false;
 int patch_instruction(u32 *addr, struct ppc_inst instr)
 {
 	/* Make sure we aren't patching a freed init section */
-	if (!skip_addr_verif && !kernel_text_address((unsigned long)addr))
+	if (!skip_addr_verif && !kernel_text_address((unsigned long)addr)) {
+		WARN_ON_ONCE(1);
 		return 0;
+	}
 
 	return do_patch_instruction(addr, instr);
 }

-- 
2.23.0

Use the existing test function for code patching tests instead of
writing to the stack. This means the address verification does not have
to be bypassed for these tests.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/lib/code-patching.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 70247fc58b6e..babf6b22adef 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c

@@ -422,9 +422,11 @@ static void __init test_branch_iform(void)
 {
 	int err;
 	struct ppc_inst instr;
-	u32 tmp[2];
-	u32 *iptr = tmp;
-	unsigned long addr = (unsigned long)tmp;
+	u32 *iptr;
+	unsigned long addr;
+
+	iptr = (u32 *)ppc_function_entry(test_trampoline);
+	addr = (unsigned long)iptr;
 
 	/* The simplest case, branch to self, no flags */
 	check(instr_is_branch_iform(ppc_inst(0x48000000)));

@@ -516,12 +518,12 @@ static void __init test_create_function_call(void)
 static void __init test_branch_bform(void)
 {
 	int err;
-	unsigned long addr;
 	struct ppc_inst instr;
-	u32 tmp[2];
-	u32 *iptr = tmp;
+	u32 *iptr;
+	unsigned long addr;
 	unsigned int flags;
 
+	iptr = (u32 *)ppc_function_entry(test_trampoline);
 	addr = (unsigned long)iptr;
 
 	/* The simplest case, branch to self, no flags */

@@ -603,6 +605,12 @@ static void __init test_translate_branch(void)
 	if (!buf)
 		return;
 
+	/*
+	 * Have to disable the address bounds check for patch_instruction
+	 * because we are patching vmalloc space here.
+	 */
+	skip_addr_verif = true;
+
 	/* Simple case, branch to self moved a little */
 	p = buf;
 	addr = (unsigned long)p;

@@ -715,6 +723,8 @@ static void __init test_translate_branch(void)
 	check(instr_is_branch_to_addr(p, addr));
 	check(instr_is_branch_to_addr(q, addr));
 
+	skip_addr_verif = false;
+
 	/* Free the buffer we were using */
 	vfree(buf);
 }

@@ -743,13 +753,11 @@ static int __init test_code_patching(void)
 {
 	printk(KERN_DEBUG "Running code patching self-tests ...\n");
 
-	skip_addr_verif = true;
 	test_branch_iform();
 	test_branch_bform();
 	test_create_function_call();
 	test_translate_branch();
 	test_prefixed_patching();
-	skip_addr_verif = false;
 
 	return 0;
 }

-- 
2.23.0

Le 26/11/2021 à 04:22, Nicholas Piggin a écrit :

Code patching tests patch the stack and (non-module) vmalloc space now,
which falls afoul of the new address check.

The stack patching can easily be fixed, but the vmalloc patching is more
difficult. For now, add an ugly workaround to skip the check while the
test code is running.

This really looks hacky.

To skip the test, you can call do_patch_instruction() instead of calling 
patch_instruction().

Excerpts from Christophe Leroy's message of November 26, 2021 4:34 pm:

Le 26/11/2021 à 04:22, Nicholas Piggin a écrit :

quoted

Code patching tests patch the stack and (non-module) vmalloc space now,
which falls afoul of the new address check.

The stack patching can easily be fixed, but the vmalloc patching is more
difficult. For now, add an ugly workaround to skip the check while the
test code is running.

This really looks hacky.

To skip the test, you can call do_patch_instruction() instead of calling 
patch_instruction().

And make a do_patch_branch function. I thought about it, and thought 
this is sligtly easier.

Thanks,
Nick

Le 26/11/2021 à 11:27, Nicholas Piggin a écrit :

Excerpts from Christophe Leroy's message of November 26, 2021 4:34 pm:

quoted

Le 26/11/2021 à 04:22, Nicholas Piggin a écrit :

quoted

Code patching tests patch the stack and (non-module) vmalloc space now,
which falls afoul of the new address check.

The stack patching can easily be fixed, but the vmalloc patching is more
difficult. For now, add an ugly workaround to skip the check while the
test code is running.

This really looks hacky.

To skip the test, you can call do_patch_instruction() instead of calling
patch_instruction().

And make a do_patch_branch function. I thought about it, and thought
this is sligtly easier.

Anyway, as reported by Sachin the ftrace code also trips in the new 
verification. So I have submitted a patch to revert to the previous 
level of verification.

Then we can fix all this properly without going through a temporary hack 
and activate the verification again once every caller is fixed.

I was not able to reproduce Sachin's problem on PPC32. Could it be 
specific to PPC64 ?

Christophe