| Message ID | 20230703143820.152479-1-matteorizzo@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/slub: refactor freelist to use custom type | expand |
On Mon, 3 Jul 2023, Matteo Rizzo wrote: > From: Jann Horn <jannh@google.com> > > Currently the SLUB code represents encoded freelist entries as "void*". > That's misleading, those things are encoded under > CONFIG_SLAB_FREELIST_HARDENED so that they're not actually dereferencable. > > Give them their own type, and split freelist_ptr() into one function per > direction (one for encoding, one for decoding). > I don't feel strongly about this. > Signed-off-by: Jann Horn <jannh@google.com> > Co-developed-by: Matteo Rizzo <matteorizzo@google.com> > Signed-off-by: Matteo Rizzo <matteorizzo@google.com> > --- > include/linux/slub_def.h | 6 ++++++ > mm/slub.c | 37 ++++++++++++++++++++++++++----------- > 2 files changed, 32 insertions(+), 11 deletions(-) > > diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h > index deb90cf4bffb..c747820a55b4 100644 > --- a/include/linux/slub_def.h > +++ b/include/linux/slub_def.h > @@ -43,6 +43,12 @@ enum stat_item { > }; > > #ifndef CONFIG_SLUB_TINY > +/* > + * freeptr_t represents a SLUB freelist pointer, which might be encoded > + * and not dereferenceable if CONFIG_SLAB_FREELIST_HARDENED is enabled. > + */ > +typedef struct { unsigned long v; } freeptr_t; Seems strange this would only appear for configs without CONFIG_SLUB_TINY. Since lots of files include linux/slab.h I think this may start to be used in non-slab code. Not sure why it needs to be added to the header file? > + > /* > * When changing the layout, make sure freelist and tid are still compatible > * with this_cpu_cmpxchg_double() alignment requirements. > diff --git a/mm/slub.c b/mm/slub.c > index e3b5d5c0eb3a..26d0ca02b61d 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -365,8 +365,8 @@ static struct workqueue_struct *flushwq; > * with an XOR of the address where the pointer is held and a per-cache > * random number. > */ > -static inline void *freelist_ptr(const struct kmem_cache *s, void *ptr, > - unsigned long ptr_addr) > +static inline freeptr_t freelist_ptr_encode(const struct kmem_cache *s, > + void *ptr, unsigned long ptr_addr) > { > #ifdef CONFIG_SLAB_FREELIST_HARDENED > /* > @@ -379,25 +379,40 @@ static inline void *freelist_ptr(const struct kmem_cache *s, void *ptr, > * calls get_freepointer() with an untagged pointer, which causes the > * freepointer to be restored incorrectly. > */ > - return (void *)((unsigned long)ptr ^ s->random ^ > - swab((unsigned long)kasan_reset_tag((void *)ptr_addr))); > + return (freeptr_t){.v = (unsigned long)ptr ^ s->random ^ > + swab((unsigned long)kasan_reset_tag((void *)ptr_addr))}; > #else > - return ptr; > + return (freeptr_t){.v = (unsigned long)ptr}; > #endif > } > > +static inline void *freelist_ptr_decode(const struct kmem_cache *s, > + freeptr_t ptr, unsigned long ptr_addr) > +{ > + void *decoded; > + > +#ifdef CONFIG_SLAB_FREELIST_HARDENED > + /* See the comment in freelist_ptr_encode */ > + decoded = (void *)(ptr.v ^ s->random ^ > + swab((unsigned long)kasan_reset_tag((void *)ptr_addr))); > +#else > + decoded = (void *)ptr.v; > +#endif > + return decoded; > +} > + > /* Returns the freelist pointer recorded at location ptr_addr. */ > static inline void *freelist_dereference(const struct kmem_cache *s, > void *ptr_addr) > { > - return freelist_ptr(s, (void *)*(unsigned long *)(ptr_addr), > + return freelist_ptr_decode(s, *(freeptr_t *)(ptr_addr), > (unsigned long)ptr_addr); > } > > static inline void *get_freepointer(struct kmem_cache *s, void *object) > { > object = kasan_reset_tag(object); > - return freelist_dereference(s, object + s->offset); > + return freelist_dereference(s, (freeptr_t *)(object + s->offset)); > } > > #ifndef CONFIG_SLUB_TINY > @@ -421,15 +436,15 @@ __no_kmsan_checks > static inline void *get_freepointer_safe(struct kmem_cache *s, void *object) > { > unsigned long freepointer_addr; > - void *p; > + freeptr_t p; > > if (!debug_pagealloc_enabled_static()) > return get_freepointer(s, object); > > object = kasan_reset_tag(object); > freepointer_addr = (unsigned long)object + s->offset; > - copy_from_kernel_nofault(&p, (void **)freepointer_addr, sizeof(p)); > - return freelist_ptr(s, p, freepointer_addr); > + copy_from_kernel_nofault(&p, (freeptr_t *)freepointer_addr, sizeof(p)); > + return freelist_ptr_decode(s, p, freepointer_addr); > } > > static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) > @@ -441,7 +456,7 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) > #endif > > freeptr_addr = (unsigned long)kasan_reset_tag((void *)freeptr_addr); > - *(void **)freeptr_addr = freelist_ptr(s, fp, freeptr_addr); > + *(freeptr_t *)freeptr_addr = freelist_ptr_encode(s, fp, freeptr_addr); > } > > /* Loop over all objects in a slab */ > > base-commit: a901a3568fd26ca9c4a82d8bc5ed5b3ed844d451 > -- > 2.41.0.255.g8b1d071c50-goog > >
Hi Matteo,
kernel test robot noticed the following build errors:
[auto build test ERROR on a901a3568fd26ca9c4a82d8bc5ed5b3ed844d451]
url: https://github.com/intel-lab-lkp/linux/commits/Matteo-Rizzo/mm-slub-refactor-freelist-to-use-custom-type/20230703-223944
base: a901a3568fd26ca9c4a82d8bc5ed5b3ed844d451
patch link: https://lore.kernel.org/r/20230703143820.152479-1-matteorizzo%40google.com
patch subject: [PATCH] mm/slub: refactor freelist to use custom type
config: arm-randconfig-r001-20230703 (https://download.01.org/0day-ci/archive/20230704/202307041252.XCQcx0eb-lkp@intel.com/config)
compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project.git 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
reproduce: (https://download.01.org/0day-ci/archive/20230704/202307041252.XCQcx0eb-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202307041252.XCQcx0eb-lkp@intel.com/
All errors (new ones prefixed by >>):
mm/slub.c:368:15: error: unknown type name 'freeptr_t'
static inline freeptr_t freelist_ptr_encode(const struct kmem_cache *s,
^
>> mm/slub.c:385:10: error: use of undeclared identifier 'freeptr_t'
return (freeptr_t){.v = (unsigned long)ptr};
^
mm/slub.c:390:6: error: unknown type name 'freeptr_t'
freeptr_t ptr, unsigned long ptr_addr)
^
>> mm/slub.c:408:45: error: expected expression
return freelist_ptr_decode(s, *(freeptr_t *)(ptr_addr),
^
mm/slub.c:408:34: error: use of undeclared identifier 'freeptr_t'
return freelist_ptr_decode(s, *(freeptr_t *)(ptr_addr),
^
mm/slub.c:415:45: error: expected expression
return freelist_dereference(s, (freeptr_t *)(object + s->offset));
^
mm/slub.c:415:34: error: use of undeclared identifier 'freeptr_t'
return freelist_dereference(s, (freeptr_t *)(object + s->offset));
^
mm/slub.c:439:2: error: use of undeclared identifier 'freeptr_t'
freeptr_t p;
^
mm/slub.c:446:43: error: expected expression
copy_from_kernel_nofault(&p, (freeptr_t *)freepointer_addr, sizeof(p));
^
mm/slub.c:446:32: error: use of undeclared identifier 'freeptr_t'
copy_from_kernel_nofault(&p, (freeptr_t *)freepointer_addr, sizeof(p));
^
>> mm/slub.c:446:69: error: use of undeclared identifier 'p'
copy_from_kernel_nofault(&p, (freeptr_t *)freepointer_addr, sizeof(p));
^
mm/slub.c:446:28: error: use of undeclared identifier 'p'
copy_from_kernel_nofault(&p, (freeptr_t *)freepointer_addr, sizeof(p));
^
mm/slub.c:447:32: error: use of undeclared identifier 'p'
return freelist_ptr_decode(s, p, freepointer_addr);
^
mm/slub.c:459:15: error: expected expression
*(freeptr_t *)freeptr_addr = freelist_ptr_encode(s, fp, freeptr_addr);
^
mm/slub.c:459:4: error: use of undeclared identifier 'freeptr_t'
*(freeptr_t *)freeptr_addr = freelist_ptr_encode(s, fp, freeptr_addr);
^
mm/slub.c:2285:15: warning: variable 'partial_slabs' set but not used [-Wunused-but-set-variable]
unsigned int partial_slabs = 0;
^
1 warning and 15 errors generated.
vim +/freeptr_t +385 mm/slub.c
358
359 /********************************************************************
360 * Core slab cache functions
361 *******************************************************************/
362
363 /*
364 * Returns freelist pointer (ptr). With hardening, this is obfuscated
365 * with an XOR of the address where the pointer is held and a per-cache
366 * random number.
367 */
> 368 static inline freeptr_t freelist_ptr_encode(const struct kmem_cache *s,
369 void *ptr, unsigned long ptr_addr)
370 {
371 #ifdef CONFIG_SLAB_FREELIST_HARDENED
372 /*
373 * When CONFIG_KASAN_SW/HW_TAGS is enabled, ptr_addr might be tagged.
374 * Normally, this doesn't cause any issues, as both set_freepointer()
375 * and get_freepointer() are called with a pointer with the same tag.
376 * However, there are some issues with CONFIG_SLUB_DEBUG code. For
377 * example, when __free_slub() iterates over objects in a cache, it
378 * passes untagged pointers to check_object(). check_object() in turns
379 * calls get_freepointer() with an untagged pointer, which causes the
380 * freepointer to be restored incorrectly.
381 */
382 return (freeptr_t){.v = (unsigned long)ptr ^ s->random ^
383 swab((unsigned long)kasan_reset_tag((void *)ptr_addr))};
384 #else
> 385 return (freeptr_t){.v = (unsigned long)ptr};
386 #endif
387 }
388
389 static inline void *freelist_ptr_decode(const struct kmem_cache *s,
390 freeptr_t ptr, unsigned long ptr_addr)
391 {
392 void *decoded;
393
394 #ifdef CONFIG_SLAB_FREELIST_HARDENED
395 /* See the comment in freelist_ptr_encode */
396 decoded = (void *)(ptr.v ^ s->random ^
397 swab((unsigned long)kasan_reset_tag((void *)ptr_addr)));
398 #else
399 decoded = (void *)ptr.v;
400 #endif
401 return decoded;
402 }
403
404 /* Returns the freelist pointer recorded at location ptr_addr. */
405 static inline void *freelist_dereference(const struct kmem_cache *s,
406 void *ptr_addr)
407 {
> 408 return freelist_ptr_decode(s, *(freeptr_t *)(ptr_addr),
409 (unsigned long)ptr_addr);
410 }
411
412 static inline void *get_freepointer(struct kmem_cache *s, void *object)
413 {
414 object = kasan_reset_tag(object);
415 return freelist_dereference(s, (freeptr_t *)(object + s->offset));
416 }
417
418 #ifndef CONFIG_SLUB_TINY
419 static void prefetch_freepointer(const struct kmem_cache *s, void *object)
420 {
421 prefetchw(object + s->offset);
422 }
423 #endif
424
425 /*
426 * When running under KMSAN, get_freepointer_safe() may return an uninitialized
427 * pointer value in the case the current thread loses the race for the next
428 * memory chunk in the freelist. In that case this_cpu_cmpxchg_double() in
429 * slab_alloc_node() will fail, so the uninitialized value won't be used, but
430 * KMSAN will still check all arguments of cmpxchg because of imperfect
431 * handling of inline assembly.
432 * To work around this problem, we apply __no_kmsan_checks to ensure that
433 * get_freepointer_safe() returns initialized memory.
434 */
435 __no_kmsan_checks
436 static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
437 {
438 unsigned long freepointer_addr;
> 439 freeptr_t p;
440
441 if (!debug_pagealloc_enabled_static())
442 return get_freepointer(s, object);
443
444 object = kasan_reset_tag(object);
445 freepointer_addr = (unsigned long)object + s->offset;
> 446 copy_from_kernel_nofault(&p, (freeptr_t *)freepointer_addr, sizeof(p));
447 return freelist_ptr_decode(s, p, freepointer_addr);
448 }
449
On Mon, 3 Jul 2023 at 22:10, David Rientjes <rientjes@google.com> wrote: > Seems strange this would only appear for configs without CONFIG_SLUB_TINY. > > Since lots of files include linux/slab.h I think this may start to be used > in non-slab code. Not sure why it needs to be added to the header file? > Thanks for the comments! I think that makes sense. I will move the typedef to slub.c and move it out of the ifdef (since that also broke the build with SLUB_TINY). -- Matteo
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h index deb90cf4bffb..c747820a55b4 100644 --- a/include/linux/slub_def.h +++ b/include/linux/slub_def.h @@ -43,6 +43,12 @@ enum stat_item { }; #ifndef CONFIG_SLUB_TINY +/* + * freeptr_t represents a SLUB freelist pointer, which might be encoded + * and not dereferenceable if CONFIG_SLAB_FREELIST_HARDENED is enabled. + */ +typedef struct { unsigned long v; } freeptr_t; + /* * When changing the layout, make sure freelist and tid are still compatible * with this_cpu_cmpxchg_double() alignment requirements. diff --git a/mm/slub.c b/mm/slub.c index e3b5d5c0eb3a..26d0ca02b61d 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -365,8 +365,8 @@ static struct workqueue_struct *flushwq; * with an XOR of the address where the pointer is held and a per-cache * random number. */ -static inline void *freelist_ptr(const struct kmem_cache *s, void *ptr, - unsigned long ptr_addr) +static inline freeptr_t freelist_ptr_encode(const struct kmem_cache *s, + void *ptr, unsigned long ptr_addr) { #ifdef CONFIG_SLAB_FREELIST_HARDENED /* @@ -379,25 +379,40 @@ static inline void *freelist_ptr(const struct kmem_cache *s, void *ptr, * calls get_freepointer() with an untagged pointer, which causes the * freepointer to be restored incorrectly. */ - return (void *)((unsigned long)ptr ^ s->random ^ - swab((unsigned long)kasan_reset_tag((void *)ptr_addr))); + return (freeptr_t){.v = (unsigned long)ptr ^ s->random ^ + swab((unsigned long)kasan_reset_tag((void *)ptr_addr))}; #else - return ptr; + return (freeptr_t){.v = (unsigned long)ptr}; #endif } +static inline void *freelist_ptr_decode(const struct kmem_cache *s, + freeptr_t ptr, unsigned long ptr_addr) +{ + void *decoded; + +#ifdef CONFIG_SLAB_FREELIST_HARDENED + /* See the comment in freelist_ptr_encode */ + decoded = (void *)(ptr.v ^ s->random ^ + swab((unsigned long)kasan_reset_tag((void *)ptr_addr))); +#else + decoded = (void *)ptr.v; +#endif + return decoded; +} + /* Returns the freelist pointer recorded at location ptr_addr. */ static inline void *freelist_dereference(const struct kmem_cache *s, void *ptr_addr) { - return freelist_ptr(s, (void *)*(unsigned long *)(ptr_addr), + return freelist_ptr_decode(s, *(freeptr_t *)(ptr_addr), (unsigned long)ptr_addr); } static inline void *get_freepointer(struct kmem_cache *s, void *object) { object = kasan_reset_tag(object); - return freelist_dereference(s, object + s->offset); + return freelist_dereference(s, (freeptr_t *)(object + s->offset)); } #ifndef CONFIG_SLUB_TINY @@ -421,15 +436,15 @@ __no_kmsan_checks static inline void *get_freepointer_safe(struct kmem_cache *s, void *object) { unsigned long freepointer_addr; - void *p; + freeptr_t p; if (!debug_pagealloc_enabled_static()) return get_freepointer(s, object); object = kasan_reset_tag(object); freepointer_addr = (unsigned long)object + s->offset; - copy_from_kernel_nofault(&p, (void **)freepointer_addr, sizeof(p)); - return freelist_ptr(s, p, freepointer_addr); + copy_from_kernel_nofault(&p, (freeptr_t *)freepointer_addr, sizeof(p)); + return freelist_ptr_decode(s, p, freepointer_addr); } static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) @@ -441,7 +456,7 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) #endif freeptr_addr = (unsigned long)kasan_reset_tag((void *)freeptr_addr); - *(void **)freeptr_addr = freelist_ptr(s, fp, freeptr_addr); + *(freeptr_t *)freeptr_addr = freelist_ptr_encode(s, fp, freeptr_addr); } /* Loop over all objects in a slab */