2021-03-04 17:52:02

by Marco Elver

Subject: [PATCH mm] kfence: fix reports if constant function prefixes exist

Some architectures prefix all functions with a constant string ('.' on
ppc64). Add ARCH_FUNC_PREFIX, which may optionally be defined in
<asm/kfence.h>, so that get_stack_skipnr() can work properly.

Link: https://lkml.kernel.org/r/[email protected]
Reported-by: Christophe Leroy <[email protected]>
Tested-by: Christophe Leroy <[email protected]>
Signed-off-by: Marco Elver <[email protected]>
---
mm/kfence/report.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/mm/kfence/report.c b/mm/kfence/report.c
index 519f037720f5..e3f71451ad9e 100644
--- a/mm/kfence/report.c
+++ b/mm/kfence/report.c
@@ -20,6 +20,11 @@

#include "kfence.h"

+/* May be overridden by <asm/kfence.h>. */
+#ifndef ARCH_FUNC_PREFIX
+#define ARCH_FUNC_PREFIX ""
+#endif
+
extern bool no_hash_pointers;

/* Helper function to either print to a seq_file or to console. */
@@ -67,8 +72,9 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries
for (skipnr = 0; skipnr < num_entries; skipnr++) {
int len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skipnr]);

- if (str_has_prefix(buf, "kfence_") || str_has_prefix(buf, "__kfence_") ||
- !strncmp(buf, "__slab_free", len)) {
+ if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfence_") ||
+ str_has_prefix(buf, ARCH_FUNC_PREFIX "__kfence_") ||
+ !strncmp(buf, ARCH_FUNC_PREFIX "__slab_free", len)) {
/*
* In case of tail calls from any of the below
* to any of the above.
@@ -77,10 +83,10 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries
}

/* Also the *_bulk() variants by only checking prefixes. */
- if (str_has_prefix(buf, "kfree") ||
- str_has_prefix(buf, "kmem_cache_free") ||
- str_has_prefix(buf, "__kmalloc") ||
- str_has_prefix(buf, "kmem_cache_alloc"))
+ if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfree") ||
+ str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_free") ||
+ str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmalloc") ||
+ str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_alloc"))
goto found;
}
if (fallback < num_entries)
--
2.30.1.766.gb4fecdf3b7-goog

2021-03-04 17:53:02

by Marco Elver

Subject: Re: [PATCH mm] kfence: fix reports if constant function prefixes exist

On Thu, 4 Mar 2021 at 15:40, Marco Elver <[email protected]> wrote:
> Some architectures prefix all functions with a constant string ('.' on
> ppc64). Add ARCH_FUNC_PREFIX, which may optionally be defined in
> <asm/kfence.h>, so that get_stack_skipnr() can work properly.
>
> Link: https://lkml.kernel.org/r/[email protected]
> Reported-by: Christophe Leroy <[email protected]>
> Tested-by: Christophe Leroy <[email protected]>
> Signed-off-by: Marco Elver <[email protected]>
> ---

For further context, the corresponding ppc64-enablement patch is was
just sent by Christophe:

https://lkml.kernel.org/r/afaec81a551ef15345cb7d7563b3fac3d7041c3a.1614868445.git.christophe.leroy@csgroup.eu

But there is no strict dependency between the patches, only that the
stack traces that KFENCE prints aren't as pretty without the
ARCH_FUNC_PREFIX patch.

So it should be fine to take them through different trees, as long as
they both make the next merge window.

Thanks,
-- Marco