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

[Alexander Potapenko <glider@google.com>]

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?

>                 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
>


-- 
Alexander Potapenko
Software Engineer

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