Messages in this thread Patch in this message | | | Subject | [PATCH 11/24] x86/msr: Restrict MSR access when the kernel is locked down | From | David Howells <> | Date | Wed, 11 Apr 2018 17:25:51 +0100 |
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From: Matthew Garrett <mjg59@srcf.ucam.org>
Writing to MSRs should not be allowed if the kernel is locked down, since it could lead to execution of arbitrary code in kernel mode. Based on a patch by Kees Cook.
MSR accesses are logged for the purposes of building up a whitelist as per Alan Cox's suggestion.
Signed-off-by: Matthew Garrett <mjg59@srcf.ucam.org> Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Kees Cook <keescook@chromium.org> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com> cc: x86@kernel.org ---
arch/x86/kernel/msr.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c index ef688804f80d..dfb61d358196 100644 --- a/arch/x86/kernel/msr.c +++ b/arch/x86/kernel/msr.c @@ -84,6 +84,11 @@ static ssize_t msr_write(struct file *file, const char __user *buf, int err = 0; ssize_t bytes = 0; + if (kernel_is_locked_down("Direct MSR access")) { + pr_info("Direct access to MSR %x\n", reg); + return -EPERM; + } + if (count % 8) return -EINVAL; /* Invalid chunk size */ @@ -135,6 +140,11 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg) err = -EFAULT; break; } + if (kernel_is_locked_down("Direct MSR access")) { + pr_info("Direct access to MSR %x\n", regs[1]); /* Display %ecx */ + err = -EPERM; + break; + } err = wrmsr_safe_regs_on_cpu(cpu, regs); if (err) break;
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