x86/mm/pkeys: Actually enable Memory Protection Keys in the CPU

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@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20160212210229.6708027C@viggo.jf.intel.com
[ Small readability edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a37b5bb03e517545e48fe79f4d49919523c34414..acf467d44e39becc610690d9df329200e2d11a47 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -976,6 +976,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                        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

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a719ad7551d20ed0e5559e50eb25b16109b4857e..4fac2634ba19157409ed1cc2c79fb7a8b7957aee 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -303,6 +303,48 @@ static __always_inline void setup_smap(struct cpuinfo_x86 *c)
        }
 }
 
+/*
+ * Protection Keys are not available in 32-bit mode.
+ */
+static bool pku_disabled;
+
+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
@@ -960,6 +1002,7 @@ static void identify_cpu(struct cpuinfo_x86 *c)
        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