From: Andrey Konovalov <andreyknvl@google.com>
The current implementation of the extra_bits interface is confusing:
passing extra_bits to __stack_depot_save makes it seem that the extra
bits are somehow stored in stack depot. In reality, they are only
embedded into a stack depot handle and are not used within stack depot.
Drop the extra_bits argument from __stack_depot_save and instead provide
a new stack_depot_set_extra_bits function (similar to the exsiting
stack_depot_get_extra_bits) that saves extra bits into a stack depot
handle.
Update the callers of __stack_depot_save to use the new interace.
This change also fixes a minor issue in the old code: __stack_depot_save
does not return NULL if saving stack trace fails and extra_bits is used.
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
include/linux/stackdepot.h | 4 +++-
lib/stackdepot.c | 38 +++++++++++++++++++++++++++++---------
mm/kasan/common.c | 2 +-
mm/kmsan/core.c | 10 +++++++---
4 files changed, 40 insertions(+), 14 deletions(-)
diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index c4e3abc16b16..f999811c66d7 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -57,7 +57,6 @@ static inline int stack_depot_early_init(void) { return 0; }
depot_stack_handle_t __stack_depot_save(unsigned long *entries,
unsigned int nr_entries,
- unsigned int extra_bits,
gfp_t gfp_flags, bool can_alloc);
depot_stack_handle_t stack_depot_save(unsigned long *entries,
@@ -71,6 +70,9 @@ void stack_depot_print(depot_stack_handle_t stack);
int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
int spaces);
+depot_stack_handle_t stack_depot_set_extra_bits(depot_stack_handle_t handle,
+ unsigned int extra_bits);
+
unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle);
#endif
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 7282565722f2..f291ad6a4e72 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -346,7 +346,6 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
*
* @entries: Pointer to storage array
* @nr_entries: Size of the storage array
- * @extra_bits: Flags to store in unused bits of depot_stack_handle_t
* @alloc_flags: Allocation gfp flags
* @can_alloc: Allocate stack slabs (increased chance of failure if false)
*
@@ -358,10 +357,6 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
* If the stack trace in @entries is from an interrupt, only the portion up to
* interrupt entry is saved.
*
- * Additional opaque flags can be passed in @extra_bits, stored in the unused
- * bits of the stack handle, and retrieved using stack_depot_get_extra_bits()
- * without calling stack_depot_fetch().
- *
* Context: Any context, but setting @can_alloc to %false is required if
* alloc_pages() cannot be used from the current context. Currently
* this is the case from contexts where neither %GFP_ATOMIC nor
@@ -371,7 +366,6 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
*/
depot_stack_handle_t __stack_depot_save(unsigned long *entries,
unsigned int nr_entries,
- unsigned int extra_bits,
gfp_t alloc_flags, bool can_alloc)
{
struct stack_record *found = NULL, **bucket;
@@ -461,8 +455,6 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
if (found)
retval.handle = found->handle.handle;
fast_exit:
- retval.extra = extra_bits;
-
return retval.handle;
}
EXPORT_SYMBOL_GPL(__stack_depot_save);
@@ -483,7 +475,7 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
unsigned int nr_entries,
gfp_t alloc_flags)
{
- return __stack_depot_save(entries, nr_entries, 0, alloc_flags, true);
+ return __stack_depot_save(entries, nr_entries, alloc_flags, true);
}
EXPORT_SYMBOL_GPL(stack_depot_save);
@@ -566,6 +558,34 @@ int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
}
EXPORT_SYMBOL_GPL(stack_depot_snprint);
+/**
+ * stack_depot_set_extra_bits - Set extra bits in a stack depot handle
+ *
+ * @handle: Stack depot handle
+ * @extra_bits: Value to set the extra bits
+ *
+ * Return: Stack depot handle with extra bits set
+ *
+ * Stack depot handles have a few unused bits, which can be used for storing
+ * user-specific information. These bits are transparent to the stack depot.
+ */
+depot_stack_handle_t stack_depot_set_extra_bits(depot_stack_handle_t handle,
+ unsigned int extra_bits)
+{
+ union handle_parts parts = { .handle = handle };
+
+ parts.extra = extra_bits;
+ return parts.handle;
+}
+EXPORT_SYMBOL(stack_depot_set_extra_bits);
+
+/**
+ * stack_depot_get_extra_bits - Retrieve extra bits from a stack depot handle
+ *
+ * @handle: Stack depot handle with extra bits saved
+ *
+ * Return: Extra bits retrieved from the stack depot handle
+ */
unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
{
union handle_parts parts = { .handle = handle };
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 833bf2cfd2a3..50f4338b477f 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -43,7 +43,7 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
unsigned int nr_entries;
nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
- return __stack_depot_save(entries, nr_entries, 0, flags, can_alloc);
+ return __stack_depot_save(entries, nr_entries, flags, can_alloc);
}
void kasan_set_track(struct kasan_track *track, gfp_t flags)
diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c
index 112dce135c7f..f710257d6867 100644
--- a/mm/kmsan/core.c
+++ b/mm/kmsan/core.c
@@ -69,13 +69,15 @@ depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
{
unsigned long entries[KMSAN_STACK_DEPTH];
unsigned int nr_entries;
+ depot_stack_handle_t handle;
nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0);
/* Don't sleep (see might_sleep_if() in __alloc_pages_nodemask()). */
flags &= ~__GFP_DIRECT_RECLAIM;
- return __stack_depot_save(entries, nr_entries, extra, flags, true);
+ handle = __stack_depot_save(entries, nr_entries, flags, true);
+ return stack_depot_set_extra_bits(handle, extra);
}
/* Copy the metadata following the memmove() behavior. */
@@ -215,6 +217,7 @@ depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
u32 extra_bits;
int depth;
bool uaf;
+ depot_stack_handle_t handle;
if (!id)
return id;
@@ -250,8 +253,9 @@ depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
* positives when __stack_depot_save() passes it to instrumented code.
*/
kmsan_internal_unpoison_memory(entries, sizeof(entries), false);
- return __stack_depot_save(entries, ARRAY_SIZE(entries), extra_bits,
- GFP_ATOMIC, true);
+ handle = __stack_depot_save(entries, ARRAY_SIZE(entries), GFP_ATOMIC,
+ true);
+ return stack_depot_set_extra_bits(handle, extra_bits);
}
void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b,
--
2.25.1> This change also fixes a minor issue in the old code: __stack_depot_save
> does not return NULL if saving stack trace fails and extra_bits is used.
Good catch!
> + *
> + * Stack depot handles have a few unused bits, which can be used for storing
> + * user-specific information. These bits are transparent to the stack depot.
> + */
> +depot_stack_handle_t stack_depot_set_extra_bits(depot_stack_handle_t handle,
> + unsigned int extra_bits)
> +{
> + union handle_parts parts = { .handle = handle };
> +
> + parts.extra = extra_bits;
> + return parts.handle;
> +}
> +EXPORT_SYMBOL(stack_depot_set_extra_bits);
You'd need to check for handle==NULL here, otherwise we're in the same
situation when __stack_depot_save returns NULL and we are happily
applying extra bits on top of it.
On Mon, 30 Jan 2023 at 21:51, <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> The current implementation of the extra_bits interface is confusing:
> passing extra_bits to __stack_depot_save makes it seem that the extra
> bits are somehow stored in stack depot. In reality, they are only
> embedded into a stack depot handle and are not used within stack depot.
>
> Drop the extra_bits argument from __stack_depot_save and instead provide
> a new stack_depot_set_extra_bits function (similar to the exsiting
> stack_depot_get_extra_bits) that saves extra bits into a stack depot
> handle.
>
> Update the callers of __stack_depot_save to use the new interace.
>
> This change also fixes a minor issue in the old code: __stack_depot_save
> does not return NULL if saving stack trace fails and extra_bits is used.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
> include/linux/stackdepot.h | 4 +++-
> lib/stackdepot.c | 38 +++++++++++++++++++++++++++++---------
> mm/kasan/common.c | 2 +-
> mm/kmsan/core.c | 10 +++++++---
> 4 files changed, 40 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
> index c4e3abc16b16..f999811c66d7 100644
> --- a/include/linux/stackdepot.h
> +++ b/include/linux/stackdepot.h
> @@ -57,7 +57,6 @@ static inline int stack_depot_early_init(void) { return 0; }
>
> depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> unsigned int nr_entries,
> - unsigned int extra_bits,
> gfp_t gfp_flags, bool can_alloc);
>
> depot_stack_handle_t stack_depot_save(unsigned long *entries,
> @@ -71,6 +70,9 @@ void stack_depot_print(depot_stack_handle_t stack);
> int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
> int spaces);
>
> +depot_stack_handle_t stack_depot_set_extra_bits(depot_stack_handle_t handle,
> + unsigned int extra_bits);
Can you add __must_check to this function? Either that or making
handle an in/out param, as otherwise it might be easy to think that it
doesn't return anything ("set_foo()" seems like it sets the
information in the handle-associated data but not handle itself ... in
case someone missed the documentation).
> unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle);
>
> #endif
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 7282565722f2..f291ad6a4e72 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -346,7 +346,6 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
> *
> * @entries: Pointer to storage array
> * @nr_entries: Size of the storage array
> - * @extra_bits: Flags to store in unused bits of depot_stack_handle_t
> * @alloc_flags: Allocation gfp flags
> * @can_alloc: Allocate stack slabs (increased chance of failure if false)
> *
> @@ -358,10 +357,6 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
> * If the stack trace in @entries is from an interrupt, only the portion up to
> * interrupt entry is saved.
> *
> - * Additional opaque flags can be passed in @extra_bits, stored in the unused
> - * bits of the stack handle, and retrieved using stack_depot_get_extra_bits()
> - * without calling stack_depot_fetch().
> - *
> * Context: Any context, but setting @can_alloc to %false is required if
> * alloc_pages() cannot be used from the current context. Currently
> * this is the case from contexts where neither %GFP_ATOMIC nor
> @@ -371,7 +366,6 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
> */
> depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> unsigned int nr_entries,
> - unsigned int extra_bits,
> gfp_t alloc_flags, bool can_alloc)
> {
> struct stack_record *found = NULL, **bucket;
> @@ -461,8 +455,6 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> if (found)
> retval.handle = found->handle.handle;
> fast_exit:
> - retval.extra = extra_bits;
> -
> return retval.handle;
> }
> EXPORT_SYMBOL_GPL(__stack_depot_save);
> @@ -483,7 +475,7 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
> unsigned int nr_entries,
> gfp_t alloc_flags)
> {
> - return __stack_depot_save(entries, nr_entries, 0, alloc_flags, true);
> + return __stack_depot_save(entries, nr_entries, alloc_flags, true);
> }
> EXPORT_SYMBOL_GPL(stack_depot_save);
>
> @@ -566,6 +558,34 @@ int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
> }
> EXPORT_SYMBOL_GPL(stack_depot_snprint);
>
> +/**
> + * stack_depot_set_extra_bits - Set extra bits in a stack depot handle
> + *
> + * @handle: Stack depot handle
> + * @extra_bits: Value to set the extra bits
> + *
> + * Return: Stack depot handle with extra bits set
> + *
> + * Stack depot handles have a few unused bits, which can be used for storing
> + * user-specific information. These bits are transparent to the stack depot.
> + */
> +depot_stack_handle_t stack_depot_set_extra_bits(depot_stack_handle_t handle,
> + unsigned int extra_bits)
> +{
> + union handle_parts parts = { .handle = handle };
> +
> + parts.extra = extra_bits;
> + return parts.handle;
> +}
> +EXPORT_SYMBOL(stack_depot_set_extra_bits);
> +
> +/**
> + * stack_depot_get_extra_bits - Retrieve extra bits from a stack depot handle
> + *
> + * @handle: Stack depot handle with extra bits saved
> + *
> + * Return: Extra bits retrieved from the stack depot handle
> + */
> unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
> {
> union handle_parts parts = { .handle = handle };
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 833bf2cfd2a3..50f4338b477f 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -43,7 +43,7 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
> unsigned int nr_entries;
>
> nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> - return __stack_depot_save(entries, nr_entries, 0, flags, can_alloc);
> + return __stack_depot_save(entries, nr_entries, flags, can_alloc);
> }
>
> void kasan_set_track(struct kasan_track *track, gfp_t flags)
> diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c
> index 112dce135c7f..f710257d6867 100644
> --- a/mm/kmsan/core.c
> +++ b/mm/kmsan/core.c
> @@ -69,13 +69,15 @@ depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
> {
> unsigned long entries[KMSAN_STACK_DEPTH];
> unsigned int nr_entries;
> + depot_stack_handle_t handle;
>
> nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0);
>
> /* Don't sleep (see might_sleep_if() in __alloc_pages_nodemask()). */
> flags &= ~__GFP_DIRECT_RECLAIM;
>
> - return __stack_depot_save(entries, nr_entries, extra, flags, true);
> + handle = __stack_depot_save(entries, nr_entries, flags, true);
> + return stack_depot_set_extra_bits(handle, extra);
> }
>
> /* Copy the metadata following the memmove() behavior. */
> @@ -215,6 +217,7 @@ depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
> u32 extra_bits;
> int depth;
> bool uaf;
> + depot_stack_handle_t handle;
>
> if (!id)
> return id;
> @@ -250,8 +253,9 @@ depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
> * positives when __stack_depot_save() passes it to instrumented code.
> */
> kmsan_internal_unpoison_memory(entries, sizeof(entries), false);
> - return __stack_depot_save(entries, ARRAY_SIZE(entries), extra_bits,
> - GFP_ATOMIC, true);
> + handle = __stack_depot_save(entries, ARRAY_SIZE(entries), GFP_ATOMIC,
> + true);
> + return stack_depot_set_extra_bits(handle, extra_bits);
> }
>
> void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b,
> --
> 2.25.1
>
On Tue, Jan 31, 2023 at 9:54 AM Marco Elver <elver@google.com> wrote:
>
> > +depot_stack_handle_t stack_depot_set_extra_bits(depot_stack_handle_t handle,
> > + unsigned int extra_bits);
>
> Can you add __must_check to this function? Either that or making
> handle an in/out param, as otherwise it might be easy to think that it
> doesn't return anything ("set_foo()" seems like it sets the
> information in the handle-associated data but not handle itself ... in
> case someone missed the documentation).
Makes sense, will do in v2 if Alexander doesn't object to the
interface change. Thanks!
On Tue, Jan 31, 2023 at 7:58 PM Andrey Konovalov <andreyknvl@gmail.com> wrote:
>
> On Tue, Jan 31, 2023 at 9:54 AM Marco Elver <elver@google.com> wrote:
> >
> > > +depot_stack_handle_t stack_depot_set_extra_bits(depot_stack_handle_t handle,
> > > + unsigned int extra_bits);
> >
> > Can you add __must_check to this function? Either that or making
> > handle an in/out param, as otherwise it might be easy to think that it
> > doesn't return anything ("set_foo()" seems like it sets the
> > information in the handle-associated data but not handle itself ... in
> > case someone missed the documentation).
>
> Makes sense, will do in v2 if Alexander doesn't object to the
> interface change. Thanks!
I do not object. Thanks for doing this!
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