Alan Cox <gno...@lxorguk.ukuu.org.uk> wrote:

> There are a load of standard tools that use this so I think you are going
> to need a whitelist. Can you at least log *which* MSR in the failing case
> so a whitelist can be built over time ?

Will the attached change work for you?

David
---
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index a05a97863286..f18cadbc31ce 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -84,8 +84,10 @@ 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"))
+       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 +137,7 @@ static long msr_ioctl(struct file *file, unsigned int ioc, 
unsigned long arg)
                        break;
                }
                if (kernel_is_locked_down("Direct MSR access")) {
+                       pr_info("Direct access to MSR %x\n", reg[1]); /* 
Display %ecx */
                        err = -EPERM;
                        break;
                }
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