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linux-user: Honor elf alignment when placing images

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Most binaries don't actually depend on more than page alignment,
but any binary can request it.  Not honoring this was a bug.

This became obvious when gdb reported

    Failed to read a valid object file image from memory

when examining some vdso which are marked as needing more
than page alignment.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2024-11-12 11:32:01 -08:00
parent 779f30a01a
commit c81d1fafa6
1 changed files with 28 additions and 7 deletions
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35
linux-user/elfload.c
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@ -3179,7 +3179,8 @@ static void load_elf_image(const char *image_name, const ImageSource *src,
char **pinterp_name)
{
g_autofree struct elf_phdr *phdr = NULL;
abi_ulong load_addr, load_bias, loaddr, hiaddr, error;
abi_ulong load_addr, load_bias, loaddr, hiaddr, error, align;
size_t reserve_size, align_size;
int i, prot_exec;
Error *err = NULL;
@ -3263,6 +3264,9 @@ static void load_elf_image(const char *image_name, const ImageSource *src,
load_addr = loaddr;
align = pow2ceil(info->alignment);
info->alignment = align;
if (pinterp_name != NULL) {
if (ehdr->e_type == ET_EXEC) {
/*
@ -3271,8 +3275,6 @@ static void load_elf_image(const char *image_name, const ImageSource *src,
*/
probe_guest_base(image_name, loaddr, hiaddr);
} else {
abi_ulong align;
/*
* The binary is dynamic, but we still need to
* select guest_base. In this case we pass a size.
@ -3290,10 +3292,7 @@ static void load_elf_image(const char *image_name, const ImageSource *src,
* Since we do not have complete control over the guest
* address space, we prefer the kernel to choose some address
* rather than force the use of LOAD_ADDR via MAP_FIXED.
* But without MAP_FIXED we cannot guarantee alignment,
* only suggest it.
*/
align = pow2ceil(info->alignment);
if (align) {
load_addr &= -align;
}
@ -3317,13 +3316,35 @@ static void load_elf_image(const char *image_name, const ImageSource *src,
* In both cases, we will overwrite pages in this range with mappings
* from the executable.
*/
load_addr = target_mmap(load_addr, (size_t)hiaddr - loaddr + 1, PROT_NONE,
reserve_size = (size_t)hiaddr - loaddr + 1;
align_size = reserve_size;
if (ehdr->e_type != ET_EXEC && align > qemu_real_host_page_size()) {
align_size += align - 1;
}
load_addr = target_mmap(load_addr, align_size, PROT_NONE,
MAP_PRIVATE | MAP_ANON | MAP_NORESERVE |
(ehdr->e_type == ET_EXEC ? MAP_FIXED_NOREPLACE : 0),
-1, 0);
if (load_addr == -1) {
goto exit_mmap;
}
if (align_size != reserve_size) {
abi_ulong align_addr = ROUND_UP(load_addr, align);
abi_ulong align_end = align_addr + reserve_size;
abi_ulong load_end = load_addr + align_size;
if (align_addr != load_addr) {
target_munmap(load_addr, align_addr - load_addr);
}
if (align_end != load_end) {
target_munmap(align_end, load_end - align_end);
}
load_addr = align_addr;
}
load_bias = load_addr - loaddr;
if (elf_is_fdpic(ehdr)) {