[PATCH 11/24] x86/msr: Restrict MSR access when the kernel is locked down
From: David Howells <dhowells@redhat.com>
Date: 2018-04-11 16:25:57
Also in:
linux-man, linux-security-module, lkml
Subsystem:
cpuid/msr driver, the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
"H. Peter Anvin", Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
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 <redacted> Reviewed-by: Thomas Gleixner <redacted> 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;