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    SubjectRe: [PATCH v3 2/5] x86/microcode/intel: Allow a late-load only if a min rev is specified

    * Ashok Raj <ashok.raj@intel.com> 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/
    >
    > 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
    > 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
    > are removed with respect to an earlier version of the microcode.
    >
    > Pseudocode for late-load is as follows:
    >
    > 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.
    > 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
    >
    > 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
    >
    > 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)
    > struct extended_sigtable *ext_header = NULL;
    > u32 sum, orig_sum, ext_sigcount = 0, i;
    > struct extended_signature *ext_sig;
    > + struct ucode_cpu_info uci;
    >
    > total_size = get_totalsize(mc_header);
    > data_size = get_datasize(mc_header);
    > @@ -248,6 +249,25 @@ static int microcode_sanity_check(void *mc, int print_err)
    > return -EINVAL;
    > }
    >
    > + /*
    > + * Enforce for late-load that min_req_id is specified in the header.
    > + * Otherwise its an old format microcode, reject it.

    s/its
    /it's

    ...

    > + */
    > + if (print_err) {
    > + if (!mc_header->min_req_id) {
    > + pr_warn("Header MUST specify min version for late-load\n");
    > + return -EINVAL;
    > + }
    > +
    > + intel_cpu_collect_info(&uci);
    > + if (uci.cpu_sig.rev < mc_header->min_req_id) {
    > + pr_warn("Current revision 0x%x is too old to update,"
    > + "must be at 0x%x version or higher\n",
    > + uci.cpu_sig.rev, mc_header->min_req_id);

    Please don't line-break user-visible syslog strings, just because
    checkpatch is stupid.

    If the user sees it as a single line, developers should see that same line
    too...

    Thanks,

    Ingo

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