On 11 March 2015 at 18:06, Andrew Jones <[email protected]> wrote:
> + if (is_aa64) {
> + switch (regime_el(env, mmu_idx)) {
> + case 1:
> + if (is_user && !(user_rw & PAGE_READ)) {
> + wxn = 0;
I still can't figure out the point of this.
This conditional will only be true if this is a
user access and user_rw is zero (indicating a page which
is neither readable nor writeable)...
> + } else if (!is_user) {
> + xn = pxn || (user_rw & PAGE_WRITE);
> + }
> + break;
> + case 2:
> + case 3:
> + break;
> + }
> + } else if (arm_feature(env, ARM_FEATURE_V7)) {
> + switch (regime_el(env, mmu_idx)) {
> + case 1:
> + case 3:
> + if (is_user) {
> + xn = xn || !(user_rw & PAGE_READ);
> + } else {
> + int uwxn = 0;
> + if (have_wxn) {
> + uwxn = regime_sctlr(env, mmu_idx) & SCTLR_UWXN;
> + }
> + xn = xn || !(prot_rw & PAGE_READ) || pxn ||
> + (uwxn && (user_rw & PAGE_WRITE));
> + }
> + break;
> + case 2:
> + break;
> + }
> + } else {
> + xn = wxn = 0;
> + }
...and in that code path the only place wxn is used
later is in this check:
> + if (xn || (wxn && (prot_rw & PAGE_WRITE))) {
...but in that case, we know that user_rw == prot_rw,
and (prot_rw & PAGE_WRITE) must be zero. So the
"(wxn && (prot_rw & PAGE_WRITE))" part of the condition
must be false, regardless of whether wxn is true or
false.
So why did we bother changing wxn in the code above?
> + return prot_rw;
> + }
> + return prot_rw | PAGE_EXEC;
> +}
I don't see what I'm missing...
thanks
-- PMM
