Messages in this thread Patch in this message | | | From | Ashok Raj <> | Subject | [PATCH v1 Part2 5/5] x86/microcode: Provide an option to override minrev enforcement | Date | Fri, 13 Jan 2023 09:29:20 -0800 |
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Minimum Required Revision (minrev) is enforced strictly. All new patches will have a minrev that is not zero. But there might be a transition time for some that need this enforcement to be relaxed.
When the override is enabled, the kernel will be tainted.
Provide a debugfs variable to override the minrev enforcement.
Signed-off-by: Ashok Raj <ashok.raj@intel.com> Cc: LKML <linux-kernel@vger.kernel.org> Cc: x86 <x86@kernel.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Tony Luck <tony.luck@intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Alison Schofield <alison.schofield@intel.com> Cc: Reinette Chatre <reinette.chatre@intel.com> Cc: Thomas Gleixner (Intel) <tglx@linutronix.de> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Stefan Talpalaru <stefantalpalaru@yahoo.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Rafael J. Wysocki <rafael@kernel.org> Cc: Peter Zilstra (Intel) <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Andrew Cooper <Andrew.Cooper3@citrix.com> --- This patch is optional. --- arch/x86/include/asm/microcode.h | 2 ++ arch/x86/kernel/cpu/microcode/core.c | 13 ++++++++++++- arch/x86/kernel/cpu/microcode/intel.c | 8 ++++++++ 3 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/microcode.h b/arch/x86/include/asm/microcode.h index 3d48143e84a9..d82f22d50ebd 100644 --- a/arch/x86/include/asm/microcode.h +++ b/arch/x86/include/asm/microcode.h @@ -16,6 +16,8 @@ struct ucode_patch { extern struct list_head microcode_cache; +extern bool override_minrev; + struct cpu_signature { unsigned int sig; unsigned int pf; diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c index 446ddf3fcc29..5ed60c6c8e8d 100644 --- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -24,6 +24,7 @@ #include <linux/miscdevice.h> #include <linux/capability.h> #include <linux/firmware.h> +#include <linux/debugfs.h> #include <linux/kernel.h> #include <linux/delay.h> #include <linux/mutex.h> @@ -44,7 +45,9 @@ #define DRIVER_VERSION "2.2" static struct microcode_ops *microcode_ops; +static struct dentry *dentry_ucode; static bool dis_ucode_ldr = true; +bool override_minrev; bool initrd_gone; @@ -497,7 +500,11 @@ static ssize_t reload_store(struct device *dev, pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n"); pr_err("You should switch to early loading, if possible.\n"); ret = -EINVAL; - goto put; + + if (!override_minrev) + goto put; + + pr_err("Overriding minrev\n"); } tmp_ret = microcode_ops->request_microcode_fw(bsp, µcode_pdev->dev); @@ -688,7 +695,11 @@ static int __init microcode_init(void) cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "x86/microcode:online", mc_cpu_online, mc_cpu_down_prep); + dentry_ucode = debugfs_create_dir("microcode", NULL); + debugfs_create_bool("override_minrev", 0644, dentry_ucode, &override_minrev); + pr_info("Microcode Update Driver: v%s.", DRIVER_VERSION); + pr_info("Override minrev %s\n", override_minrev ? "enabled" : "disabled"); return 0; diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c index 68a3c5569cd2..172e1f166844 100644 --- a/arch/x86/kernel/cpu/microcode/intel.c +++ b/arch/x86/kernel/cpu/microcode/intel.c @@ -141,6 +141,14 @@ static int is_lateload_safe(struct microcode_header_intel *mc_header) { struct ucode_cpu_info uci; + /* + * If minrev is bypassed via debugfs, then allow late-load. + */ + if (override_minrev) { + pr_info("Bypassing minrev enforcement via debugfs\n"); + return 0; + } + /* * When late-loading, ensure the header declares a minimum revision * required to perform a late-load. -- 2.34.1
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