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target/arm: Improve IMPDEF algorithm for IRG

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When GCR_EL1.RRND==1, the choosing of the random value is IMPDEF,
and the kernel is not expected to have set RGSR_EL1.  Force a
non-zero value into SEED, so that we do not continually return
the same tag.

Reported-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200724163853.504655-4-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Richard Henderson 2020-07-27 16:12:11 +01:00 committed by Peter Maydell
parent 7ad01d78a9
commit d4f6dda182
1 changed files with 30 additions and 7 deletions
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37
target/arm/mte_helper.c
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@ -24,6 +24,8 @@
#include "exec/ram_addr.h"
#include "exec/cpu_ldst.h"
#include "exec/helper-proto.h"
#include "qapi/error.h"
#include "qemu/guest-random.h"
static int choose_nonexcluded_tag(int tag, int offset, uint16_t exclude)
@ -211,16 +213,37 @@ static uint8_t *allocation_tag_mem(CPUARMState *env, int ptr_mmu_idx,
uint64_t HELPER(irg)(CPUARMState *env, uint64_t rn, uint64_t rm)
{
int rtag;
/*
* Our IMPDEF choice for GCR_EL1.RRND==1 is to behave as if
* GCR_EL1.RRND==0, always producing deterministic results.
*/
uint16_t exclude = extract32(rm | env->cp15.gcr_el1, 0, 16);
int rrnd = extract32(env->cp15.gcr_el1, 16, 1);
int start = extract32(env->cp15.rgsr_el1, 0, 4);
int seed = extract32(env->cp15.rgsr_el1, 8, 16);
int offset, i;
int offset, i, rtag;
/*
* Our IMPDEF choice for GCR_EL1.RRND==1 is to continue to use the
* deterministic algorithm. Except that with RRND==1 the kernel is
* not required to have set RGSR_EL1.SEED != 0, which is required for
* the deterministic algorithm to function. So we force a non-zero
* SEED for that case.
*/
if (unlikely(seed == 0) && rrnd) {
do {
Error *err = NULL;
uint16_t two;
if (qemu_guest_getrandom(&two, sizeof(two), &err) < 0) {
/*
* Failed, for unknown reasons in the crypto subsystem.
* Best we can do is log the reason and use a constant seed.
*/
qemu_log_mask(LOG_UNIMP, "IRG: Crypto failure: %s\n",
error_get_pretty(err));
error_free(err);
two = 1;
}
seed = two;
} while (seed == 0);
}
/* RandomTag */
for (i = offset = 0; i < 4; ++i) {