Messages in this thread Patch in this message | | | Subject | Re: WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4), by kmemleak's scan_block() | From | Pekka Enberg <> | Date | Tue, 25 Aug 2009 12:11:47 +0300 |
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On Tue, 2009-08-25 at 11:03 +0200, Vegard Nossum wrote: > I don't know so much about the kmemleak internals, but this I can say > about the kmemcheck part: According to your definition, an object is > initialized if all the bytes of an object are initialized. > > Is it possible that because of this, if we have a partially > uninitialized object, kmemleak will not record the pointers found in > that object? If so, it might skip valid pointers, and deem an object > unreferenced. Which could make kmemleak give false-positives. > > I think it would be better to ask kmemcheck on a per-pointer basis > (i.e. for each pointer-sized word in the object), whether it is > initialized or not.
Yeah, makes sense.
Pekka
diff --git a/arch/x86/mm/kmemcheck/kmemcheck.c b/arch/x86/mm/kmemcheck/kmemcheck.c index 2c55ed0..528bf95 100644 --- a/arch/x86/mm/kmemcheck/kmemcheck.c +++ b/arch/x86/mm/kmemcheck/kmemcheck.c @@ -331,6 +331,20 @@ static void kmemcheck_read_strict(struct pt_regs *regs, kmemcheck_shadow_set(shadow, size); } +bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size) +{ + enum kmemcheck_shadow status; + void *shadow; + + shadow = kmemcheck_shadow_lookup(addr); + if (!shadow) + return true; + + status = kmemcheck_shadow_test(shadow, size); + + return status == KMEMCHECK_SHADOW_INITIALIZED; +} + /* Access may cross page boundary */ static void kmemcheck_read(struct pt_regs *regs, unsigned long addr, unsigned int size) diff --git a/include/linux/kmemcheck.h b/include/linux/kmemcheck.h index 47b39b7..dc2fd54 100644 --- a/include/linux/kmemcheck.h +++ b/include/linux/kmemcheck.h @@ -34,6 +34,8 @@ void kmemcheck_mark_initialized_pages(struct page *p, unsigned int n); int kmemcheck_show_addr(unsigned long address); int kmemcheck_hide_addr(unsigned long address); +bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size); + #else #define kmemcheck_enabled 0 @@ -99,6 +101,11 @@ static inline void kmemcheck_mark_initialized_pages(struct page *p, { } +static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size) +{ + return true; +} + #endif /* CONFIG_KMEMCHECK */ /* diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 6debe0d..b075bf0 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -97,6 +97,7 @@ #include <asm/processor.h> #include <asm/atomic.h> +#include <linux/kmemcheck.h> #include <linux/kmemleak.h> /* @@ -885,7 +886,8 @@ static void scan_block(void *_start, void *_end, for (ptr = start; ptr < end; ptr++) { unsigned long flags; - unsigned long pointer = *ptr; + unsigned long pointer; + struct kmemleak_object *object; if (allow_resched) @@ -893,6 +895,13 @@ static void scan_block(void *_start, void *_end, if (scan_should_stop()) break; + /* Don't scan uninitialized memory. */ + if (!kmemcheck_is_obj_initialized((unsigned long) ptr, + sizeof(unsigned long))) + continue; + + pointer = *ptr; + object = find_and_get_object(pointer, 1); if (!object) continue;
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