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kasan: improve kasan_non_canonical_hook 

Make kasan_non_canonical_hook to be more sure in its report (i.e.  say
"probably" instead of "maybe") if the address belongs to the shadow memory
region for kernel addresses.

Also use the kasan_shadow_to_mem helper to calculate the original address.

Also improve the comments in kasan_non_canonical_hook.

Link: https://lkml.kernel.org/r/af94ef3cb26f8c065048b3158d9f20f6102bfaaa.1703188911.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Andrey Konovalov 2023-12-21 21:04:45 +01:00 committed by Andrew Morton
parent 5cb6674b69
commit c20e3feadd
2 changed files with 26 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
mm/kasan/kasan.h
View File

@ -307,6 +307,12 @@ struct kasan_stack_ring {
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
static __always_inline bool addr_in_shadow(const void *addr)
{
return addr >= (void *)KASAN_SHADOW_START &&
addr < (void *)KASAN_SHADOW_END;
}
#ifndef kasan_shadow_to_mem
static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
{

34
mm/kasan/report.c
View File

@ -635,37 +635,43 @@ void kasan_report_async(void)
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
/*
* With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
* canonical half of the address space) cause out-of-bounds shadow memory reads
* before the actual access. For addresses in the low canonical half of the
* address space, as well as most non-canonical addresses, that out-of-bounds
* shadow memory access lands in the non-canonical part of the address space.
* Help the user figure out what the original bogus pointer was.
* With compiler-based KASAN modes, accesses to bogus pointers (outside of the
* mapped kernel address space regions) cause faults when KASAN tries to check
* the shadow memory before the actual memory access. This results in cryptic
* GPF reports, which are hard for users to interpret. This hook helps users to
* figure out what the original bogus pointer was.
*/
void kasan_non_canonical_hook(unsigned long addr)
{
unsigned long orig_addr;
const char *bug_type;
/*
* All addresses that came as a result of the memory-to-shadow mapping
* (even for bogus pointers) must be >= KASAN_SHADOW_OFFSET.
*/
if (addr < KASAN_SHADOW_OFFSET)
return;
orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
orig_addr = (unsigned long)kasan_shadow_to_mem((void *)addr);
/*
* For faults near the shadow address for NULL, we can be fairly certain
* that this is a KASAN shadow memory access.
* For faults that correspond to shadow for low canonical addresses, we
* can still be pretty sure - that shadow region is a fairly narrow
* chunk of the non-canonical address space.
* But faults that look like shadow for non-canonical addresses are a
* really large chunk of the address space. In that case, we still
* print the decoded address, but make it clear that this is not
* necessarily what's actually going on.
* For faults that correspond to the shadow for low or high canonical
* addresses, we can still be pretty sure: these shadow regions are a
* fairly narrow chunk of the address space.
* But the shadow for non-canonical addresses is a really large chunk
* of the address space. For this case, we still print the decoded
* address, but make it clear that this is not necessarily what's
* actually going on.
*/
if (orig_addr < PAGE_SIZE)
bug_type = "null-ptr-deref";
else if (orig_addr < TASK_SIZE)
bug_type = "probably user-memory-access";
else if (addr_in_shadow((void *)addr))
bug_type = "probably wild-memory-access";
else
bug_type = "maybe wild-memory-access";
pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,