Re: [PATCH 2/4] kfence: add function to mask address bits

[Sven Schnelle <svens@linux.ibm.com>]

Alexander Potapenko <glider@google.com> writes:

> On Wed, Jul 28, 2021 at 9:03 PM Heiko Carstens <hca@linux.ibm.com> wrote:
>>
>> From: Sven Schnelle <svens@linux.ibm.com>
>>
>> s390 only reports the page address during a translation fault.
>> To make the kfence unit tests pass, add a function that might
>> be implemented by architectures to mask out address bits.
>>
>> Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
>> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
>> ---
>>  mm/kfence/kfence_test.c | 13 ++++++++++++-
>>  1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
>> index 942cbc16ad26..eb6307c199ea 100644
>> --- a/mm/kfence/kfence_test.c
>> +++ b/mm/kfence/kfence_test.c
>> @@ -23,8 +23,15 @@
>>  #include <linux/tracepoint.h>
>>  #include <trace/events/printk.h>
>>
>> +#include <asm/kfence.h>
>> +
>>  #include "kfence.h"
>>
>> +/* May be overridden by <asm/kfence.h>. */
>> +#ifndef arch_kfence_test_address
>> +#define arch_kfence_test_address(addr) (addr)
>> +#endif
>> +
>>  /* Report as observed from console. */
>>  static struct {
>>         spinlock_t lock;
>> @@ -82,6 +89,7 @@ static const char *get_access_type(const struct expect_report *r)
>>  /* Check observed report matches information in @r. */
>>  static bool report_matches(const struct expect_report *r)
>>  {
>> +       unsigned long addr = (unsigned long)r->addr;
>>         bool ret = false;
>>         unsigned long flags;
>>         typeof(observed.lines) expect;
>> @@ -131,22 +139,25 @@ static bool report_matches(const struct expect_report *r)
>>         switch (r->type) {
>>         case KFENCE_ERROR_OOB:
>>                 cur += scnprintf(cur, end - cur, "Out-of-bounds %s at", get_access_type(r));
>> +               addr = arch_kfence_test_address(addr);
>
> Can we normalize addr once before (or after) this switch?
>

I don't think so. When reporing corrupted memory or an invalid free the
address is not generated by hardware but kfence itself, and therefore we
would strip valid bits.

>>                 break;
>>         case KFENCE_ERROR_UAF:
>>                 cur += scnprintf(cur, end - cur, "Use-after-free %s at", get_access_type(r));
>> +               addr = arch_kfence_test_address(addr);
>>                 break;
>>         case KFENCE_ERROR_CORRUPTION:
>>                 cur += scnprintf(cur, end - cur, "Corrupted memory at");
>>                 break;
>>         case KFENCE_ERROR_INVALID:
>>                 cur += scnprintf(cur, end - cur, "Invalid %s at", get_access_type(r));
>> +               addr = arch_kfence_test_address(addr);
>>                 break;
>>         case KFENCE_ERROR_INVALID_FREE:
>>                 cur += scnprintf(cur, end - cur, "Invalid free of");
>>                 break;
>>         }
>>
>> -       cur += scnprintf(cur, end - cur, " 0x%p", (void *)r->addr);
>> +       cur += scnprintf(cur, end - cur, " 0x%p", (void *)addr);
>>
>>         spin_lock_irqsave(&observed.lock, flags);
>>         if (!report_available())
>> --
>> 2.25.1
>>