[PATCH V40 13/29] x86/msr: Restrict MSR access when the kernel is locked down
From: Matthew Garrett <hidden>
Date: 2019-08-20 00:18:50
Also in:
linux-security-module, lkml
Subsystem:
cpuid/msr driver, lockdown security module, security subsystem, the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
"H. Peter Anvin", Nicolas Bouchinet, Xiu Jianfeng, Paul Moore, James Morris, "Serge E. Hallyn", 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. Signed-off-by: Matthew Garrett <redacted> Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Kees Cook <redacted> Reviewed-by: Thomas Gleixner <redacted> cc: x86@kernel.org Signed-off-by: James Morris <jmorris@namei.org> --- arch/x86/kernel/msr.c | 8 ++++++++ include/linux/security.h | 1 + security/lockdown/lockdown.c | 1 + 3 files changed, 10 insertions(+)
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 3db2252b958d..1547be359d7f 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c@@ -34,6 +34,7 @@ #include <linux/notifier.h> #include <linux/uaccess.h> #include <linux/gfp.h> +#include <linux/security.h> #include <asm/cpufeature.h> #include <asm/msr.h>
@@ -79,6 +80,10 @@ static ssize_t msr_write(struct file *file, const char __user *buf, int err = 0; ssize_t bytes = 0; + err = security_locked_down(LOCKDOWN_MSR); + if (err) + return err; + if (count % 8) return -EINVAL; /* Invalid chunk size */
@@ -130,6 +135,9 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg) err = -EFAULT; break; } + err = security_locked_down(LOCKDOWN_MSR); + if (err) + break; err = wrmsr_safe_regs_on_cpu(cpu, regs); if (err) break;
diff --git a/include/linux/security.h b/include/linux/security.h
index cd93fa5d3c6d..010637a79eac 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h@@ -109,6 +109,7 @@ enum lockdown_reason { LOCKDOWN_HIBERNATION, LOCKDOWN_PCI_ACCESS, LOCKDOWN_IOPORT, + LOCKDOWN_MSR, LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_CONFIDENTIALITY_MAX, };
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 8b7d65dbb086..b1c1c72440d5 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c@@ -24,6 +24,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_HIBERNATION] = "hibernation", [LOCKDOWN_PCI_ACCESS] = "direct PCI access", [LOCKDOWN_IOPORT] = "raw io port access", + [LOCKDOWN_MSR] = "raw MSR access", [LOCKDOWN_INTEGRITY_MAX] = "integrity", [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", };
--
2.23.0.rc1.153.gdeed80330f-goog