On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > Some users (currently only KMSAN) may want to use spare bits in > depot_stack_handle_t. Let them do so by adding @extra_bits to > __stack_depot_save() to store arbitrary flags, and providing > stack_depot_get_extra_bits() to retrieve those flags. > > Also adapt KASAN to the new prototype by passing extra_bits=0, as KASAN > does not intend to store additional information in the stack handle. > > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> > --- > v4: > -- per Marco Elver's request, fold "kasan: common: adapt to the new > prototype of __stack_depot_save()" into this patch to prevent > bisection breakages. > > Link: https://linux-review.googlesource.com/id/I0587f6c777667864768daf07821d594bce6d8ff9 > --- > include/linux/stackdepot.h | 8 ++++++++ > lib/stackdepot.c | 29 ++++++++++++++++++++++++----- > mm/kasan/common.c | 2 +- > 3 files changed, 33 insertions(+), 6 deletions(-) > > diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h > index bc2797955de90..9ca7798d7a318 100644 > --- a/include/linux/stackdepot.h > +++ b/include/linux/stackdepot.h > @@ -14,9 +14,15 @@ > #include <linux/gfp.h> > > typedef u32 depot_stack_handle_t; > +/* > + * Number of bits in the handle that stack depot doesn't use. Users may store > + * information in them. > + */ > +#define STACK_DEPOT_EXTRA_BITS 5 > > 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); > > /* > @@ -59,6 +65,8 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries, > unsigned int stack_depot_fetch(depot_stack_handle_t handle, > unsigned long **entries); > > +unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle); > + > int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size, > int spaces); > > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > index 5ca0d086ef4a3..3d1dbdd5a87f6 100644 > --- a/lib/stackdepot.c > +++ b/lib/stackdepot.c > @@ -42,7 +42,8 @@ > #define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \ > STACK_ALLOC_ALIGN) > #define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \ > - STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS) > + STACK_ALLOC_NULL_PROTECTION_BITS - \ > + STACK_ALLOC_OFFSET_BITS - STACK_DEPOT_EXTRA_BITS) > #define STACK_ALLOC_SLABS_CAP 8192 > #define STACK_ALLOC_MAX_SLABS \ > (((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \ > @@ -55,6 +56,7 @@ union handle_parts { > u32 slabindex : STACK_ALLOC_INDEX_BITS; > u32 offset : STACK_ALLOC_OFFSET_BITS; > u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS; > + u32 extra : STACK_DEPOT_EXTRA_BITS; > }; > }; > > @@ -76,6 +78,14 @@ static int next_slab_inited; > static size_t depot_offset; > static DEFINE_RAW_SPINLOCK(depot_lock); > > +unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle) > +{ > + union handle_parts parts = { .handle = handle }; > + > + return parts.extra; > +} > +EXPORT_SYMBOL(stack_depot_get_extra_bits); > + > static bool init_stack_slab(void **prealloc) > { > if (!*prealloc) > @@ -139,6 +149,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc) > stack->handle.slabindex = depot_index; > stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN; > stack->handle.valid = 1; > + stack->handle.extra = 0; > memcpy(stack->entries, entries, flex_array_size(stack, entries, size)); > depot_offset += required_size; > > @@ -343,6 +354,7 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch); > * > * @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) > * > @@ -354,6 +366,10 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch); > * 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 > @@ -363,10 +379,11 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch); > */ > 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; > - depot_stack_handle_t retval = 0; > + union handle_parts retval = { .handle = 0 }; > struct page *page = NULL; > void *prealloc = NULL; > unsigned long flags; > @@ -450,9 +467,11 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, > free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER); > } > if (found) > - retval = found->handle.handle; > + retval.handle = found->handle.handle; > fast_exit: > - return retval; > + retval.extra = extra_bits; > + > + return retval.handle; > } > EXPORT_SYMBOL_GPL(__stack_depot_save); > > @@ -472,6 +491,6 @@ 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, alloc_flags, true); > + return __stack_depot_save(entries, nr_entries, 0, alloc_flags, true); > } > EXPORT_SYMBOL_GPL(stack_depot_save); > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index c40c0e7b3b5f1..ba4fceeec173c 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -36,7 +36,7 @@ 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, flags, can_alloc); > + return __stack_depot_save(entries, nr_entries, 0, flags, can_alloc); > } > > void kasan_set_track(struct kasan_track *track, gfp_t flags) > -- > 2.37.0.rc0.161.g10f37bed90-goog >
