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Re: [Qemu-stable] [PATCH 1/5] multiboot: Reject kernels exceeding the ad
From: |
Jack Schwartz |
Subject: |
Re: [Qemu-stable] [PATCH 1/5] multiboot: Reject kernels exceeding the address space |
Date: |
Wed, 14 Mar 2018 22:19:27 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 |
Hi Kevin.
My comments are inline...
On 2018-03-14 10:32, Kevin Wolf wrote:
The code path with a manually set mh_load_addr in the Multiboot header
checks that load_end_addr <= load_addr, but the path where load_end_addr
is automatically detected if 0 is given in the header misses the
corresponding check.
1) The code checks that load_end_addr >= load_addr (before letting it
through).
2) load_end_addr is used only when it is read in as non-zero, so no
check is needed if zero. (It gets debug-printed even when zero, but is
used only to calculate mb_load_size and only when non-zero.)
If the kernel binary size is larger than can fit in
the address space after load_addr, we ended up with a kernel_size that
is smaller than load_size, which means that we read the file into a too
small buffer.
Add a check to reject kernel files with such Multiboot headers.
Code itself looks fine.
Modulo above comments:
Reviewed-by: Jack Schwartz <address@hidden>
Thanks,
Jack
Signed-off-by: Kevin Wolf <address@hidden>
---
hw/i386/multiboot.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/hw/i386/multiboot.c b/hw/i386/multiboot.c
index b9064264d8..1e215bf8d3 100644
--- a/hw/i386/multiboot.c
+++ b/hw/i386/multiboot.c
@@ -247,6 +247,10 @@ int load_multiboot(FWCfgState *fw_cfg,
}
mb_load_size = kernel_file_size - mb_kernel_text_offset;
}
+ if (mb_load_size > UINT32_MAX - mh_load_addr) {
+ error_report("kernel does not fit in address space");
+ exit(1);
+ }
if (mh_bss_end_addr) {
if (mh_bss_end_addr < (mh_load_addr + mb_load_size)) {
error_report("invalid bss_end_addr address");
[Qemu-stable] [PATCH 2/5] multiboot: Check validity of mh_header_addr, Kevin Wolf, 2018/03/14
[Qemu-stable] [PATCH 3/5] tests/multiboot: Test exit code for every qemu run, Kevin Wolf, 2018/03/14
[Qemu-stable] [PATCH 5/5] tests/multiboot: Add .gitignore, Kevin Wolf, 2018/03/14
[Qemu-stable] [PATCH 4/5] tests/multiboot: Add tests for the a.out kludge, Kevin Wolf, 2018/03/14