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[metal] Allow more fine-grained control over page permissions (#663)

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- use PAGE_RSRV bit (originally only for blinkenlights),
  rather than PAGE_V bit, to indicate that a virtual address
  page has been reserved — this should allow a program to
  create & reserve inaccessible "guard pages"
- mark page table entries for non-code pages with PAGE_XD bit,
  which should be supported on (circa) post-2004 x86-64 CPUs
This commit is contained in:
tkchia 2022-10-13 02:07:11 +08:00 • committed by GitHub
parent 0f89140882
commit d38700687a
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GPG key ID: 4AEE18F83AFDEB23
5 changed files with 25 additions and 14 deletions
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16
libc/intrin/mman.greg.c
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@ -71,7 +71,7 @@ noasan textreal uint64_t *__get_virtual(struct mman *mm, uint64_t *t,
for (h = 39;; h -= 9) {
e = t + ((vaddr >> h) & 511);
if (h == 12) return e;
if (!(*e & PAGE_V)) {
if (!(*e & (PAGE_V | PAGE_RSRV))) {
if (!maketables) return NULL;
if (!(p = __new_page(mm))) return NULL;
__clear_page(BANE + p);
@ -123,8 +123,8 @@ noasan textreal void __invert_memory_area(struct mman *mm, uint64_t *pml4t,
pe = ROUNDUP(pe, 4096);
for (p = ps; p != pe; p += 4096) {
m = __get_virtual(mm, pml4t, BANE + p, true);
if (m && !(*m & PAGE_V)) {
*m = p | PAGE_V | pte_flags;
if (m && !(*m & (PAGE_V | PAGE_RSRV))) {
*m = p | PAGE_V | PAGE_RSRV | pte_flags;
}
}
}
@ -139,7 +139,7 @@ static noasan textreal void __invert_memory(struct mman *mm, uint64_t *pml4t) {
/* ape/ape.S has already mapped the first 2 MiB of physical memory. */
if (ps < 0x200000 && ps + size <= 0x200000)
continue;
__invert_memory_area(mm, pml4t, ps, size, PAGE_RW);
__invert_memory_area(mm, pml4t, ps, size, PAGE_RW | PAGE_XD);
}
}
@ -187,8 +187,12 @@ noasan textreal void __map_phdrs(struct mman *mm, uint64_t *pml4t, uint64_t b) {
for (p = (struct Elf64_Phdr *)REAL(ape_phdrs), m = 0;
p < (struct Elf64_Phdr *)REAL(ape_phdrs_end); ++p) {
if (p->p_type == PT_LOAD || p->p_type == PT_GNU_STACK) {
f = PAGE_V | PAGE_U;
if (p->p_flags & PF_W) f |= PAGE_RW;
f = PAGE_RSRV | PAGE_U;
if (p->p_flags & PF_W)
f |= PAGE_V | PAGE_RW;
else if (p->p_flags & (PF_R | PF_X))
f |= PAGE_V;
if (!(p->p_flags & PF_X)) f |= PAGE_XD;
for (i = 0; i < p->p_memsz; i += 4096) {
if (i < p->p_filesz) {
v = b + p->p_offset + i;