Messages in this thread Patch in this message | | | Date | Fri, 19 Aug 2022 13:11:07 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v3 2/5] x86/microcode/intel: Allow a late-load only if a min rev is specified |
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On Wed, Aug 17, 2022 at 05:11:24AM +0000, Ashok Raj wrote: > In general users don't have the necessary information to determine > whether a late-load of a new microcode version has removed any feature > (MSR, CPUID etc) between what is currently loaded and this new microcode. > To address this issue, Intel has added a "minimum required version" field to > a previously reserved field in the file header. Microcode updates > should only be applied if the current microcode version is equal > to, or greater than this minimum required version. > > https://lore.kernel.org/linux-kernel/alpine.DEB.2.21.1909062237580.1902@nanos.tec.linutronix.de/
That goes into a Link: tag.
> Thomas made some suggestions on how meta-data in the microcode file could > provide Linux with information to decide if the new microcode is suitable > candidate for late-load. But even the "simpler" option#1 requires a lot of
In all your text:
s/late-load/late loading/g
It is called CONFIG_MICROCODE_LATE_LOADING - not CONFIG_MICROCODE_LATE_LOAD.
People are confused enough already - no need for more.
> metadata and corresponding kernel code to parse it. > > The proposal here is an even simpler option. The criteria for a microcode to > be a viable late-load candidate is that no CPUID or OS visible MSR features
Simply "OS visible features" - CPUID and MSRs are only two examples. The microcode cannot change how the OS is supposed to interact with visible features because that causes problems.
> are removed with respect to an earlier version of the microcode. > > Pseudocode for late-load is as follows:
Unknown word [Pseudocode] in commit message. Suggestions: ['Pseudo code',
> if header.min_required_id == 0 > This is old format microcode, block late-load > else if current_ucode_version < header.min_required_id > Current version is too old, block late-load of this microcode. > else > OK to proceed with late-load. > > Any microcode that removes a feature will set the min_version to itself.
"... that modifies the interface to a OS-visible feature..."
> This will enforce this microcode is not suitable for late-loading. > > The enforcement is not in hardware and limited to kernel loader enforcing > the requirement. It is not required for early loading of microcode to > enforce this requirement, since the new features are only > evaluated after early loading in the boot process. > > > Test cases covered: > > 1. With new kernel, attempting to load an older format microcode with the > min_rev=0 should be blocked by kernel. > > [ 210.541802] microcode: Header MUST specify min version for late-load
Make that more user-friendly:
"microcode: Late loading denied: microcode header does not specify a required min version."
> 2. New microcode with a non-zero min_rev in the header, but the specified > min_rev is greater than what is currently loaded in the CPU should be > blocked by kernel. > > 245.139828] microcode: Current revision 0x8f685300 is too old to update, > must be at 0xaa000050 version or higher
"microcode: Late loading denied: Current version ... or higher. Use early loading instead."
> 3. New microcode with a min_rev < currently loaded should allow loading the > microcode > > 4. Build initrd with microcode that has min_rev=0, or min_rev > currently > loaded should permit early loading microcode from initrd. > > > Tested-by: William Xie <william.xie@intel.com> > Reviewed-by: Tony Luck <tony.luck@intel.com> > Signed-off-by: Ashok Raj <ashok.raj@intel.com> > --- > arch/x86/include/asm/microcode_intel.h | 4 +++- > arch/x86/kernel/cpu/microcode/intel.c | 20 ++++++++++++++++++++ > 2 files changed, 23 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h > index 4c92cea7e4b5..16b8715e0984 100644 > --- a/arch/x86/include/asm/microcode_intel.h > +++ b/arch/x86/include/asm/microcode_intel.h > @@ -14,7 +14,9 @@ struct microcode_header_intel { > unsigned int pf; > unsigned int datasize; > unsigned int totalsize; > - unsigned int reserved[3]; > + unsigned int reserved1; > + unsigned int min_req_id; > + unsigned int reserved3; > }; > > struct microcode_intel { > diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c > index c4b11e2fbe33..1eb202ec2302 100644 > --- a/arch/x86/kernel/cpu/microcode/intel.c > +++ b/arch/x86/kernel/cpu/microcode/intel.c > @@ -178,6 +178,7 @@ static int microcode_sanity_check(void *mc, int print_err)
You can't do this in this function:
load_ucode_intel_bsp -> __load_ucode_intel -> scan_microcode -> microcode_sanity_check
which is the early path.
So you'd have to pass down the fact that you're doing late loading from request_microcode_fw().
Now, I'm staring at that ugly refresh_fw bool arg in that function and I *think* I did it 10 years ago because it shouldn't try to load from the fs when it is resuming because there might not be a fs yet... or something to that effect.
tglx might have a better idea how to check we're in the ->starting notifier... -- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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