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Re: [PATCH 3/7] contrib/elf2dmp: Ensure segment fits in file


From: Akihiko Odaki
Subject: Re: [PATCH 3/7] contrib/elf2dmp: Ensure segment fits in file
Date: Tue, 5 Mar 2024 12:53:38 +0900
User-agent: Mozilla Thunderbird

On 2024/03/05 2:52, Peter Maydell wrote:
On Sun, 3 Mar 2024 at 10:53, Akihiko Odaki <akihiko.odaki@daynix.com> wrote:

This makes elf2dmp more robust against corrupted inputs.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
  contrib/elf2dmp/addrspace.c | 5 +++--
  1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/contrib/elf2dmp/addrspace.c b/contrib/elf2dmp/addrspace.c
index 980a7aa5f8fb..d546a400dfda 100644
--- a/contrib/elf2dmp/addrspace.c
+++ b/contrib/elf2dmp/addrspace.c
@@ -88,11 +88,12 @@ int pa_space_create(struct pa_space *ps, QEMU_Elf *qemu_elf)
      ps->block = g_new(struct pa_block, ps->block_nr);

      for (i = 0; i < phdr_nr; i++) {
-        if (phdr[i].p_type == PT_LOAD) {
+        if (phdr[i].p_type == PT_LOAD && phdr[i].p_offset < qemu_elf->size) {
              ps->block[block_i] = (struct pa_block) {
                  .addr = (uint8_t *)qemu_elf->map + phdr[i].p_offset,
                  .paddr = phdr[i].p_paddr,
-                .size = phdr[i].p_filesz,
+                .size = MIN(phdr[i].p_filesz,
+                            qemu_elf->size - phdr[i].p_offset),

Shouldn't "p_filesz is smaller than the actual amount of data in the
file" be a failure condition? In include/hw/elf_ops.h we treat it
that way:

             mem_size = ph->p_memsz; /* Size of the ROM */
             file_size = ph->p_filesz; /* Size of the allocated data */
             data_offset = ph->p_offset; /* Offset where the data is located */

             if (file_size > 0) {
                 if (g_mapped_file_get_length(mapped_file) <
                     file_size + data_offset) {
                     goto fail;
                 }
                 [etc]

Like that code, we could then only check if p_offset + p_filesz is off
the end of the file, rather than checking p_offset separately.

              };
              pa_block_align(&ps->block[block_i]);
              block_i = ps->block[block_i].size ? (block_i + 1) : block_i;

thanks
-- PMM

I'm making this permissive for corrupted dumps since they may still include valuable information.

It is different from include/hw/elf_ops.h, which is presumably used to load executables rather than dumps. Loading a corrupted executable does nothing good.

Regards,
Akihiko Odaki



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