Re: [Qemu-devel] [PATCH v1] tpm: check localities index

[Stefan Berger]

On 11/20/18 2:22 AM, P J P wrote:
> From: Prasad J Pandit <address@hidden>
>
> While performing mmio device r/w operations, guest could set 'addr'
> parameter such that 'locty' index exceeds TPM_TIS_NUM_LOCALITIES=5
> after setting new 'locty' via 'tpm_tis_new_active_locality'.
> Add check to avoid OOB access.
>
> Reported-by: Cheng Feng <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
> ---
>   hw/tpm/tpm_tis.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> Update: add assert() calls
>    -> https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg00912.html
>
> diff --git a/hw/tpm/tpm_tis.c b/hw/tpm/tpm_tis.c
> index 12f5c9a759..d6bf3ceb26 100644
> --- a/hw/tpm/tpm_tis.c
> +++ b/hw/tpm/tpm_tis.c
> @@ -293,6 +293,7 @@ static void tpm_tis_request_completed(TPMIf *ti, int ret)
>       uint8_t locty = s->cmd.locty;
>       uint8_t l;
>
> +    assert(TPM_TIS_IS_VALID_LOCTY(locty));


This one I may take. However, the tpm_tis_tpm_send is called with a 
valid locality (derived from the MMIO address) and passes the locality 
number to the backend. The backends are reading the locality but don't 
change it.


>       if (s->cmd.selftest_done) {
>           for (l = 0; l < TPM_TIS_NUM_LOCALITIES; l++) {
>               s->loc[locty].sts |= TPM_TIS_STS_SELFTEST_DONE;
> @@ -401,6 +402,7 @@ static uint64_t tpm_tis_mmio_read(void *opaque, hwaddr addr,
>       uint32_t avail;
>       uint8_t v;
>
> +    assert(TPM_TIS_IS_VALID_LOCTY(locty));


This check comes right after

 uint8_t locty = tpm_tis_locality_from_addr(addr);

which gives us a locty in range [0.. 4]. So I don't think a check here 
is needed.


>       if (tpm_backend_had_startup_error(s->be_driver)) {
>           return 0;
>       }
> @@ -523,6 +525,7 @@ static void tpm_tis_mmio_write(void *opaque, hwaddr addr,
>       uint16_t len;
>       uint32_t mask = (size == 1) ? 0xff : ((size == 2) ? 0xffff : ~0);
>
> +    assert(TPM_TIS_IS_VALID_LOCTY(locty));


Same comment here.

>       trace_tpm_tis_mmio_write(size, addr, val);
>
>       if (locty == 4) {
> @@ -642,7 +645,7 @@ static void tpm_tis_mmio_write(void *opaque, hwaddr addr,
>               }
>           }
>
> -        if (set_new_locty) {
> +        if (set_new_locty && TPM_TIS_IS_VALID_LOCTY(active_locty)) {

It is possible that no locality is active by the current locality 
relinquishing the ownership and we have to be able to set that.


>               tpm_tis_new_active_locality(s, active_locty);
>           }