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x86: fix page_validate for page-outs

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A non-present entry might still be valid access, the
page could just be swapped out.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2020-11-19 11:49:38 -08:00 • committed by Anas Nashif
commit 8771fbdaac
1 changed files with 18 additions and 8 deletions
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26
arch/x86/core/x86_mmu.c
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@ -1185,20 +1185,30 @@ static bool page_validate(pentry_t *ptables, uint8_t *addr, bool write)
for (int level = 0; level < NUM_LEVELS; level++) {
pentry_t entry = get_entry(table, addr, level);
if ((entry & MMU_P) == 0U) {
/* Non-present, no access.
* TODO: will need re-visiting with demand paging
* implemented, could just be paged out
*/
return false;
}
if (is_leaf(level, entry)) {
#ifdef CONFIG_X86_KPTI
if (is_flipped_pte(entry)) {
/* We flipped this to prevent user access
* since just clearing US isn't sufficient
*/
return false;
}
#endif
/* US and RW bits still carry meaning if non-present.
* If the data page is paged out, access bits are
* preserved. If un-mapped, the whole entry is 0.
*/
if (((entry & MMU_US) == 0U) ||
(write && ((entry & MMU_RW) == 0U))) {
return false;
}
} else {
if ((entry & MMU_P) == 0U) {
/* Missing intermediate table, address is
* un-mapped
*/
return false;
}
table = next_table(entry, level);
}
}