51 lines
1.7 KiB
Diff
51 lines
1.7 KiB
Diff
From: Matthew Garrett <matthew.garrett@nebula.com>
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Date: Wed, 8 Nov 2017 15:11:34 +0000
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Subject: [13/29] x86/msr: Restrict MSR access when the kernel is locked down
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Origin: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit?id=696dcddb285558b4febf318fe620a344d2b2fa47
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Writing to MSRs should not be allowed if the kernel is locked down, since
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it could lead to execution of arbitrary code in kernel mode. Based on a
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patch by Kees Cook.
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MSR accesses are logged for the purposes of building up a whitelist as per
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Alan Cox's suggestion.
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Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
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Signed-off-by: David Howells <dhowells@redhat.com>
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Acked-by: Kees Cook <keescook@chromium.org>
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Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
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Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
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cc: x86@kernel.org
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---
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arch/x86/kernel/msr.c | 10 ++++++++++
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1 file changed, 10 insertions(+)
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diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
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index ef688804f80d..dfb61d358196 100644
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--- a/arch/x86/kernel/msr.c
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+++ b/arch/x86/kernel/msr.c
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@@ -84,6 +84,11 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
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int err = 0;
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ssize_t bytes = 0;
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+ if (kernel_is_locked_down("Direct MSR access")) {
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+ pr_info("Direct access to MSR %x\n", reg);
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+ return -EPERM;
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+ }
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+
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if (count % 8)
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return -EINVAL; /* Invalid chunk size */
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@@ -135,6 +140,11 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
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err = -EFAULT;
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break;
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}
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+ if (kernel_is_locked_down("Direct MSR access")) {
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+ pr_info("Direct access to MSR %x\n", regs[1]); /* Display %ecx */
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+ err = -EPERM;
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+ break;
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+ }
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err = wrmsr_safe_regs_on_cpu(cpu, regs);
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if (err)
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break;
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