From: Andy Lutomirski <l...@kernel.org>
This is temporary. It will allow the next few patches to be tested
incrementally.
Setting unsafe_fsgsbase is a root hole. Don't do it.
Signed-off-by: Andy Lutomirski <l...@kernel.org>
[chang: Fix the deactivated flag. Add TAINT_INSECURE flag.]
Signed-off-by: Chang S. Bae <chang.seok....@intel.com>
Reviewed-by: Andi Kleen <a...@linux.intel.com>
Cc: H. Peter Anvin <h...@zytor.com>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 3 +++
arch/x86/kernel/cpu/common.c | 26 +++++++++++++++++++++++++
2 files changed, 29 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index f2040d4..b92c4a0 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2600,6 +2600,9 @@
emulation library even if a 387 maths coprocessor
is present.
+ unsafe_fsgsbase [X86] Allow FSGSBASE instructions. This will be
+ replaced with a nofsgsbase flag.
+
no_console_suspend
[HW] Never suspend the console
Disable suspending of consoles during suspend and
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0be333f..5412d62 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -356,6 +356,24 @@ static __always_inline void setup_umip(struct cpuinfo_x86
*c)
}
/*
+ * Temporary hack: FSGSBASE is unsafe until a few kernel code paths are
updated.
+ * This allows us to get the kernel ready incrementally. Setting
+ * unsafe_fsgsbase will allow the series to be bisected if necessary.
+ *
+ * Once all the pieces are in place, this will go away and be replaced with
+ * a nofsgsbase chicken flag.
+ */
+static bool unsafe_fsgsbase;
+
+static __init int setup_unsafe_fsgsbase(char *arg)
+{
+ unsafe_fsgsbase = true;
+ add_taint(TAINT_INSECURE, LOCKDEP_STILL_OK);
+ return 1;
+}
+__setup("unsafe_fsgsbase", setup_unsafe_fsgsbase);
+
+/*
* Protection Keys are not available in 32-bit mode.
*/
static bool pku_disabled;
@@ -1286,6 +1304,14 @@ static void identify_cpu(struct cpuinfo_x86 *c)
setup_smap(c);
setup_umip(c);
+ /* Enable FSGSBASE instructions if available. */
+ if (cpu_has(c, X86_FEATURE_FSGSBASE)) {
+ if (unsafe_fsgsbase)
+ cr4_set_bits(X86_CR4_FSGSBASE);
+ else
+ clear_cpu_cap(c, X86_FEATURE_FSGSBASE);
+ }
+
/*
* The vendor-specific functions might have changed features.
* Now we do "generic changes."
--
2.7.4
