From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
This sets the bit in 'cr4' to actually enable the protection
keys feature. We also include a boot-time disable for the
feature "nopku".
Seting X86_CR4_PKE will cause the X86_FEATURE_OSPKE cpuid
bit to appear set. At this point in boot, identify_cpu()
has already run the actual CPUID instructions and populated
the "cpu features" structures. We need to go back and
re-run identify_cpu() to make sure it gets updated values.
We *could* simply re-populate the 11th word of the cpuid
data, but this is probably quick enough.
Also note that with the cpu_has() check and X86_FEATURE_PKU
present in disabled-features.h, we do not need an #ifdef
for setup_pku().
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
b/Documentation/kernel-parameters.txt | 3 ++
b/arch/x86/kernel/cpu/common.c | 41 ++++++++++++++++++++++++++++++++++
2 files changed, 44 insertions(+)
diff -puN arch/x86/kernel/cpu/common.c~pkeys-50-should-be-last-patch arch/x86/kernel/cpu/common.c
--- a/arch/x86/kernel/cpu/common.c~pkeys-50-should-be-last-patch 2015-12-03 16:21:33.708037809 -0800
+++ b/arch/x86/kernel/cpu/common.c 2015-12-03 16:21:33.714038081 -0800
@@ -289,6 +289,46 @@ static __always_inline void setup_smap(s
}
/*
+ * Protection Keys are not available in 32-bit mode.
+ */
+static bool pku_disabled = false;
+static __always_inline void setup_pku(struct cpuinfo_x86 *c)
+{
+ if (!cpu_has(c, X86_FEATURE_PKU))
+ return;
+ if (pku_disabled)
+ return;
+
+ cr4_set_bits(X86_CR4_PKE);
+ /*
+ * Seting X86_CR4_PKE will cause the X86_FEATURE_OSPKE
+ * cpuid bit to be set. We need to ensure that we
+ * update that bit in this CPU's "cpu_info".
+ */
+ get_cpu_cap(c);
+}
+#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
+static __init int setup_disable_pku(char *arg)
+{
+ /*
+ * Do not clear the X86_FEATURE_PKU bit. All of the
+ * runtime checks are against OSPKE so clearing the
+ * bit does nothing.
+ *
+ * This way, we will see "pku" in cpuinfo, but not
+ * "ospke", which is exactly what we want. It shows
+ * that the CPU has PKU, but the OS has not enabled it.
+ * This happens to be exactly how a system would look
+ * if we disabled the config option.
+ */
+ pr_info("x86: 'nopku' specified, disabling Memory Protection Keys\n");
+ pku_disabled = true;
+ return 1;
+}
+__setup("nopku", setup_disable_pku);
+#endif /* CONFIG_X86_64 */
+
+/*
* Some CPU features depend on higher CPUID levels, which may not always
* be available due to CPUID level capping or broken virtualization
* software. Add those features to this table to auto-disable them.
@@ -948,6 +988,7 @@ static void identify_cpu(struct cpuinfo_
init_hypervisor(c);
x86_init_rdrand(c);
x86_init_cache_qos(c);
+ setup_pku(c);
/*
* Clear/Set all flags overriden by options, need do it
diff -puN Documentation/kernel-parameters.txt~pkeys-50-should-be-last-patch Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt~pkeys-50-should-be-last-patch 2015-12-03 16:21:33.710037900 -0800
+++ b/Documentation/kernel-parameters.txt 2015-12-03 16:21:33.715038127 -0800
@@ -958,6 +958,9 @@ bytes respectively. Such letter suffixes
See Documentation/x86/intel_mpx.txt for more
information about the feature.
+ nopku [X86] Disable Memory Protection Keys CPU feature found
+ in some Intel CPUs.
+
eagerfpu= [X86]
on enable eager fpu restore
off disable eager fpu restore
_
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