summaryrefslogtreecommitdiff
path: root/arch
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2020-08-03 17:23:49 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-03 17:23:49 -0700
commitc813e8c9dff344a3b46bc9bba8aff5a7ebbc67e7 (patch)
tree55be3425c40858ce3ae22d7f753394c95ee9c65f /arch
parent69094c20323c5efff462a2e02d0bb7b6608779ad (diff)
parenta7e1f67ed29f0c339e2aa7483d13b085127566ab (diff)
downloadlwn-c813e8c9dff344a3b46bc9bba8aff5a7ebbc67e7.tar.gz
lwn-c813e8c9dff344a3b46bc9bba8aff5a7ebbc67e7.zip
Merge tag 'x86-misc-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 MSR filtering from Ingo Molnar: "Filter MSR writes from user-space by default, and print a syslog entry if they happen outside the allowed set of MSRs, which is a single one for now, MSR_IA32_ENERGY_PERF_BIAS. The plan is to eventually disable MSR writes by default (they can still be enabled via allow_writes=on)" * tag 'x86-misc-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/msr: Filter MSR writes
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/msr.c69
1 files changed, 69 insertions, 0 deletions
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 1547be359d7f..49dcfb85e773 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -42,6 +42,14 @@
static struct class *msr_class;
static enum cpuhp_state cpuhp_msr_state;
+enum allow_write_msrs {
+ MSR_WRITES_ON,
+ MSR_WRITES_OFF,
+ MSR_WRITES_DEFAULT,
+};
+
+static enum allow_write_msrs allow_writes = MSR_WRITES_DEFAULT;
+
static ssize_t msr_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
@@ -70,6 +78,24 @@ static ssize_t msr_read(struct file *file, char __user *buf,
return bytes ? bytes : err;
}
+static int filter_write(u32 reg)
+{
+ switch (allow_writes) {
+ case MSR_WRITES_ON: return 0;
+ case MSR_WRITES_OFF: return -EPERM;
+ default: break;
+ }
+
+ if (reg == MSR_IA32_ENERGY_PERF_BIAS)
+ return 0;
+
+ pr_err_ratelimited("Write to unrecognized MSR 0x%x by %s\n"
+ "Please report to x86@kernel.org\n",
+ reg, current->comm);
+
+ return 0;
+}
+
static ssize_t msr_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
@@ -84,6 +110,10 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
if (err)
return err;
+ err = filter_write(reg);
+ if (err)
+ return err;
+
if (count % 8)
return -EINVAL; /* Invalid chunk size */
@@ -92,9 +122,13 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
err = -EFAULT;
break;
}
+
+ add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+
err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
if (err)
break;
+
tmp += 2;
bytes += 8;
}
@@ -242,6 +276,41 @@ static void __exit msr_exit(void)
}
module_exit(msr_exit)
+static int set_allow_writes(const char *val, const struct kernel_param *cp)
+{
+ /* val is NUL-terminated, see kernfs_fop_write() */
+ char *s = strstrip((char *)val);
+
+ if (!strcmp(s, "on"))
+ allow_writes = MSR_WRITES_ON;
+ else if (!strcmp(s, "off"))
+ allow_writes = MSR_WRITES_OFF;
+ else
+ allow_writes = MSR_WRITES_DEFAULT;
+
+ return 0;
+}
+
+static int get_allow_writes(char *buf, const struct kernel_param *kp)
+{
+ const char *res;
+
+ switch (allow_writes) {
+ case MSR_WRITES_ON: res = "on"; break;
+ case MSR_WRITES_OFF: res = "off"; break;
+ default: res = "default"; break;
+ }
+
+ return sprintf(buf, "%s\n", res);
+}
+
+static const struct kernel_param_ops allow_writes_ops = {
+ .set = set_allow_writes,
+ .get = get_allow_writes
+};
+
+module_param_cb(allow_writes, &allow_writes_ops, NULL, 0600);
+
MODULE_AUTHOR("H. Peter Anvin <hpa@zytor.com>");
MODULE_DESCRIPTION("x86 generic MSR driver");
MODULE_LICENSE("GPL");