Re: [PATCH v3 2/2] kasan: Add explicit preconditions to kasan_report()

On 1/22/21 2:46 PM, Andrey Konovalov wrote:

On Fri, Jan 22, 2021 at 3:38 PM Vincenzo Frascino
[off-list ref] wrote:

quoted

With the introduction of KASAN_HW_TAGS, kasan_report() dereferences
the address passed as a parameter.

It doesn't dereference the address, it accesses the metadata. And only
when addr_has_metadata() succeeds.

Yes, this is correct. Seems I forgot again to unstash something. Will fix it in v4.

quoted

Add a comment to make sure that the preconditions to the function are
explicitly clarified.

Note: An invalid address (e.g. NULL) passed to the function when,
KASAN_HW_TAGS is enabled, leads to a kernel panic.

This is no longer true, right? Commit description needs to be updated.

quoted

Cc: Andrey Ryabinin <redacted>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Leon Romanovsky <redacted>
Cc: Andrey Konovalov <redacted>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
---
 include/linux/kasan.h | 7 +++++++
 mm/kasan/kasan.h      | 2 +-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index fe1ae73ff8b5..0aea9e2a2a01 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h

@@ -333,6 +333,13 @@ static inline void *kasan_reset_tag(const void *addr)
        return (void *)arch_kasan_reset_tag(addr);
 }

+/**
+ * kasan_report - print a report about a bad memory access detected by KASAN
+ * @addr: address of the bad access
+ * @size: size of the bad access
+ * @is_write: whether the bad access is a write or a read
+ * @ip: instruction pointer for the accessibility check or the bad access itself
+ */

Looks good, thanks!

quoted

 bool kasan_report(unsigned long addr, size_t size,
                bool is_write, unsigned long ip);

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index cc4d9e1d49b1..8c706e7652f2 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h

@@ -209,7 +209,7 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,

 static inline bool addr_has_metadata(const void *addr)
 {
-       return true;
+       return (is_vmalloc_addr(addr) || virt_addr_valid(addr));
 }

Let's put this change into a separate patch.

Ok, it will be done in v4.

quoted

 #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
--
2.30.0

-- 
Regards,
Vincenzo

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