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UPSTREAM: kfence: fix is_kfence_address() for addresses below KFENCE_POOL_SIZE

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Originally the addr != NULL check was meant to take care of the case
where __kfence_pool == NULL (KFENCE is disabled).  However, this does
not work for addresses where addr > 0 && addr < KFENCE_POOL_SIZE.

This can be the case on NULL-deref where addr > 0 && addr < PAGE_SIZE or
any other faulting access with addr < KFENCE_POOL_SIZE.  While the
kernel would likely crash, the stack traces and report might be
confusing due to double faults upon KFENCE's attempt to unprotect such
an address.

Fix it by just checking that __kfence_pool != NULL instead.

Link: https://lkml.kernel.org/r/20210818130300.2482437-1-elver@google.com
Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: Marco Elver <elver@google.com>
Reported-by: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Acked-by: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>    [5.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

(cherry picked from commit a7cb5d23eaea148f8582229846f8dfff192f05c3)
Bug: 196937223
Bug: 197197917
Test: local QEMU runs with init/main.c modified to access the NULL page
Signed-off-by: Alexander Potapenko <glider@google.com>
Change-Id: I6a339e8c6b4d2bdc3ee9bd575725489a8233aade
(cherry picked from commit 228d32e2d0b730f00eb0a8950698902b3ad23daf)
This commit is contained in:
Marco Elver 2021-08-19 19:04:30 -07:00 • committed by Michael Bestas
commit c78abaa8fe
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GPG key ID: CC95044519BE6669
1 changed files with 4 additions and 3 deletions
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7
include/linux/kfence.h
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@ -51,10 +51,11 @@ extern atomic_t kfence_allocation_gate;
static __always_inline bool is_kfence_address(const void *addr)
{
/*
* The non-NULL check is required in case the __kfence_pool pointer was
* never initialized; keep it in the slow-path after the range-check.
* The __kfence_pool != NULL check is required to deal with the case
* where __kfence_pool == NULL && addr < KFENCE_POOL_SIZE. Keep it in
* the slow-path after the range-check!
*/
return unlikely((unsigned long)((char *)addr - __kfence_pool) < KFENCE_POOL_SIZE && addr);
return unlikely((unsigned long)((char *)addr - __kfence_pool) < KFENCE_POOL_SIZE && __kfence_pool);
}
/**