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

[Christian Borntraeger]

On 28.07.21 21:02, Heiko Carstens wrote:
> From: Sven Schnelle <svens@xxxxxxxxxxxxx>
>
> 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.

FWIW, the s390 hardware does indeed only provide the page address
for page faults. We had to do the same trick for other software,
e.g. see valgrind
https://sourceware.org/git/?p=valgrind.git;a=blob;f=coregrind/m_signals.c;h=b45afe59923245352ac17fdd1eeeb5e220f912be;hb=HEAD#l2702


> Signed-off-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
> Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
> ---
>   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);
>   		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())