Messages in this thread | | | Subject | Re: [PATCH v5 4/6] x86/microcode/AMD: Check microcode container data in the late loader | From | "Maciej S. Szmigiero" <> | Date | Fri, 4 May 2018 01:26:50 +0200 |
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On 03.05.2018 12:01, Borislav Petkov wrote: > On Wed, May 02, 2018 at 02:47:39AM +0200, Maciej S. Szmigiero wrote: >> On 01.05.2018 22:03, Borislav Petkov wrote: >>> On Tue, May 01, 2018 at 06:19:56PM +0200, Maciej S. Szmigiero wrote: >>>> -EINVAL cast to unsigned int is 4294967274 and this value is also >>>> a valid count of bytes to skip that this function can return. >>> >>> And where exactly in the *old* code do we do that? >> >> The old code returned this value as a signed int, but then any >> "patch_size" value (which is u32) above INT_MAX read from a section header >> wrapped around to a negative pseudo-error code (which likely didn't match >> any actual error number). > > Lemme repeat my question: *where* *exactly* in the old code do we do that? > > Feel free to paste snippets to show what you mean. >
From verify_and_add_patch(): > static int verify_and_add_patch(u8 family, u8 *fw, unsigned int leftover) > { > struct microcode_header_amd *mc_hdr; > struct ucode_patch *patch; > unsigned int patch_size, crnt_size, ret; > u32 proc_fam; > u16 proc_id; > > patch_size = *(u32 *)(fw + 4);
Here we read a u32 (= unsigned int) value from a section header and store it into an unsigned int variable.
> crnt_size = patch_size + SECTION_HDR_SIZE;
Here we add 8 (SECTION_HDR_SIZE) to this value and once again store it into an unsigned int variable.
> mc_hdr = (struct microcode_header_amd *)(fw + SECTION_HDR_SIZE); > proc_id = mc_hdr->processor_rev_id; > > proc_fam = find_cpu_family_by_equiv_cpu(proc_id); > if (!proc_fam) { > pr_err("No patch family for equiv ID: 0x%04x\n", proc_id); > return crnt_size;
Here we return this variable, implicitly converting it into a (signed) int. Any value above INT_MAX will wrap around to a negative pseudo-error code (which might not match any actual error number).
Maciej
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