mirror of
https://git.proxmox.com/git/efi-boot-shim
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809dc7a18b
Covscan says:
146 UINTN len = 0;
147 CHAR16 *b = NULL;
2. tainted_data_argument: Calling function get_file_size taints argument len.
148 rc = get_file_size(fh2, &len);
3. Condition (INTN)rc < 0, taking false branch.
149 if (EFI_ERROR(rc)) {
150 uefi_call_wrapper(fh2->Close, 1, fh2);
151 return rc;
152 }
153
4. overflow_assign: Assigning overflowed or truncated value (or a value computed from an overflowed or a truncated value) to b.
8. overflow: Add operation overflows on operands len and 2UL. Example value for operand: len = 18446744073709551614.
154 b = AllocateZeroPool(len + 2);
Technically we can't handle a file larger than 0xfffffffffffffffd (on
x86_64) because when we try to allocate the buffer to hold it with a
trailing UCS-2 NUL we overflow to 0. Also our filesystem can't hold a
file bigger than 4GB... So this is probably actually broken on 32-bit
platforms.
This patch limits it to some handy amount like 1024 * PAGE_SIZE, aka
4MB.
Note that this doesn't appear to be exploitable (at least on edk2-based
firmwares), because AllocateZeroPool() has a minimum granularity of 1
page, so even if you overflow it with a 4GB file, we'll get 1 page out
of it and then try to read 1 byte into it, and then it's just going to
be a parse error on the CSV. Even if we error on the sentinal UCS-2 NUL
we put at the end, it'll still be inside of the zeroed page, and it still
won't fault or overwrite any meaningful data.
Signed-off-by: Peter Jones <pjones@redhat.com>
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||
|---|---|---|
| Cryptlib | ||
| include | ||
| lib | ||
| .gitignore | ||
| .syntastic_c_config | ||
| buildid.c | ||
| BUILDING | ||
| cert.S | ||
| COPYRIGHT | ||
| crypt_blowfish.c | ||
| elf_aarch64_efi.lds | ||
| elf_arm_efi.lds | ||
| elf_ia32_efi.lds | ||
| elf_ia64_efi.lds | ||
| elf_x86_64_efi.lds | ||
| errlog.c | ||
| fallback.c | ||
| httpboot.c | ||
| make-certs | ||
| Make.coverity | ||
| Make.defaults | ||
| Make.rules | ||
| Make.scan-build | ||
| Makefile | ||
| model.c | ||
| MokManager.c | ||
| MokVars.txt | ||
| netboot.c | ||
| PasswordCrypt.c | ||
| README | ||
| README.fallback | ||
| README.tpm | ||
| replacements.c | ||
| shim.c | ||
| shim.h | ||
| testplan.txt | ||
| TODO | ||
| tpm.c | ||
| version.c.in | ||
| version.h | ||
shim is a trivial EFI application that, when run, attempts to open and execute another application. It will initially attempt to do this via the standard EFI LoadImage() and StartImage() calls. If these fail (because secure boot is enabled and the binary is not signed with an appropriate key, for instance) it will then validate the binary against a built-in certificate. If this succeeds and if the binary or signing key are not blacklisted then shim will relocate and execute the binary. shim will also install a protocol which permits the second-stage bootloader to perform similar binary validation. This protocol has a GUID as described in the shim.h header file and provides a single entry point. On 64-bit systems this entry point expects to be called with SysV ABI rather than MSABI, and so calls to it should not be wrapped. On systems with a TPM chip enabled and supported by the system firmware, shim will extend various PCRs with the digests of the targets it is loading. A full list is in the file README.tpm . To use shim, simply place a DER-encoded public certificate in a file such as pub.cer and build with "make VENDOR_CERT_FILE=pub.cer". There are a couple of build options, and a couple of ways to customize the build, described in BUILDING.