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[ELFLOADER] Use host page size instead of p_align for mapping ranges (#4158)

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* [ELFLOADER] Use host page size instead of p_align for mapping ranges

`p_align` only requires `p_vaddr` and `p_offset` to be congruent modulo `p_align`; segment starts need not be `p_align`-aligned. A `p_align` of 16 KiB on a host with 4 KiB pages is therefore perfectly legal. The loader, however, used `p_align` as the page mask when computing mapping and protection ranges, which makes the writable segment's range extended into pages belonging to executable code in my case.

* remove useless guard
This commit is contained in:
Yang Liu authored and GitHub committed 2026-08-03 11:55:38 +02:00
1 parent e0ae94d742
commit b5066f8ab4
1 file changed
+6 -9
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src/elfs/elfloader.c
+6 -9
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@@ -322,12 +322,9 @@ int AllocLoadElfMemory(box64context_t* context, elfheader_t* head, int mainbin)
head->multiblocks[n].align = e->p_align;
// HACK: Mark all the code pages writable in unittest mode because some tests mix code and (writable) data...
uint8_t prot = ((e->p_flags & PF_R)?PROT_READ:0)|(((e->p_flags & PF_W) || box64_unittest_mode)?PROT_WRITE:0)|((e->p_flags & PF_X)?PROT_EXEC:0);
// check if alignment is correct
uintptr_t balign = head->multiblocks[n].align-1;
if (balign < (box64_pagesize - 1)) balign = box64_pagesize - 1;
head->multiblocks[n].asize = (e->p_memsz + (e->p_paddr & balign) + (box64_pagesize - 1)) & ~(box64_pagesize - 1);
head->multiblocks[n].asize = (e->p_memsz + (e->p_paddr & (box64_pagesize - 1)) + (box64_pagesize - 1)) & ~(box64_pagesize - 1);
int try_mmap = 1;
if(e->p_paddr&balign)
if(e->p_paddr&(box64_pagesize - 1))
try_mmap = 0;
if(e->p_offset&(box64_pagesize-1))
try_mmap = 0;
@@ -359,10 +356,10 @@ int AllocLoadElfMemory(box64context_t* context, elfheader_t* head, int mainbin)
}
}
if(!try_mmap) {
uintptr_t paddr = head->multiblocks[n].paddr&~balign;
uintptr_t paddr = head->multiblocks[n].paddr&~(box64_pagesize - 1);
size_t asize = head->multiblocks[n].asize+(head->multiblocks[n].paddr-paddr);
void* p = MAP_FAILED;
if(paddr==(paddr&~(box64_pagesize-1)) && (asize==ALIGN(asize))) {
if(asize == ALIGN(asize)) {
printf_dump(log_level, "Allocating 0x%zx (0x%zx) bytes @%p, will read 0x%zx @%p for Elf \"%s\"\n", asize, e->p_memsz, (void*)paddr, e->p_filesz, (void*)head->multiblocks[n].paddr, head->name);
p = InternalMmap(
(void*)paddr,
@@ -403,7 +400,7 @@ int AllocLoadElfMemory(box64context_t* context, elfheader_t* head, int mainbin)
}
}
if(p==MAP_FAILED || p!=(void*)paddr) {
printf_log(LOG_NONE, "Cannot create memory map (@%p 0x%zx/0x%zx) for elf \"%s\"", (void*)paddr, asize, balign, head->name);
printf_log(LOG_NONE, "Cannot create memory map (@%p 0x%zx/0x%zx) for elf \"%s\"", (void*)paddr, asize, (box64_pagesize - 1), head->name);
if(p==MAP_FAILED) {
printf_log(LOG_NONE, " error=%d/%s\n", errno, strerror(errno));
} else {
@@ -416,7 +413,7 @@ int AllocLoadElfMemory(box64context_t* context, elfheader_t* head, int mainbin)
if(e->p_filesz) {
fseeko64(head->file, head->multiblocks[n].offs, SEEK_SET);
if(fread((void*)head->multiblocks[n].paddr, head->multiblocks[n].size, 1, head->file)!=1) {
printf_log(LOG_NONE, "Cannot read elf block (@%p 0x%zx/0x%zx) for elf \"%s\"\n", (void*)head->multiblocks[n].offs, head->multiblocks[n].asize, balign, head->name);
printf_log(LOG_NONE, "Cannot read elf block (@%p 0x%zx/0x%zx) for elf \"%s\"\n", (void*)head->multiblocks[n].offs, head->multiblocks[n].asize, (box64_pagesize - 1), head->name);
return 1;
}
}