Re: [PATCH 2/2] s390: mm: Fix secure storage access exception handling

Claudio Imbrenda
2021-01-19T13:09:50Z

On Tue, 19 Jan 2021 05:04:02 -0500
Janosch Frank <frankja@linux.ibm.com> wrote:

> Turns out that the bit 61 in the TEID is not always 1 and if that's
> the case the address space ID and the address are
> unpredictable. Without an address and it's address space ID we can't

*its

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> export memory and hence we can only send a SIGSEGV to the process or
> panic the kernel depending on who caused the exception.
>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> Fixes: 084ea4d611a3d ("s390/mm: add (non)secure page access
> exceptions handlers") Cc: stable@vger.kernel.org
> ---
> arch/s390/mm/fault.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index e30c7c781172..5442937e5b4b 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -791,6 +791,20 @@ void do_secure_storage_access(struct pt_regs
> *regs) struct page *page;
> int rc;
>
> + /* There are cases where we don't have a TEID. */
> + if (!(regs->int_parm_long & 0x4)) {
> + /*
> + * Userspace could for example try to execute secure
> + * storage and trigger this. We should tell it that
> it
> + * shouldn't do that.
> + */
> + if (user_mode(regs)) {
> + send_sig(SIGSEGV, current, 0);
> + return;
> + } else
> + panic("Unexpected PGM 0x3d with TEID bit
> 61=0");
> + }
> +
> switch (get_fault_type(regs)) {
> case USER_FAULT:
> mm = current->mm;