From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
Andi Kleen <ak@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Markus T Metzger <markus.t.metzger@intel.com>,
Ravi Shankar <ravi.v.shankar@intel.com>,
"Chang S . Bae" <chang.seok.bae@intel.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH v4 12/13] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2
Date: Wed, 16 Jan 2019 14:48:48 -0800 [thread overview]
Message-ID: <20190116224849.8617-13-chang.seok.bae@intel.com> (raw)
In-Reply-To: <20190116224849.8617-1-chang.seok.bae@intel.com>
From: Andi Kleen <ak@linux.intel.com>
The kernel needs to explicitly enable FSGSBASE. So, the application needs
to know if it can safely use these instructions. Just looking at the CPUID
bit is not enough because it may be running in a kernel that does not
enable the instructions.
One way for the application would be to just try and catch the SIGILL.
But that is difficult to do in libraries which may not want to overwrite
the signal handlers of the main application.
So we need to provide a way for the application to discover the kernel
capability.
I used AT_HWCAP2 in the ELF aux vector which is already used by PPC for
similar things. We define a new Linux defined bitmap returned in AT_HWCAP.
Next to MONITOR/MWAIT, bit 1 is reserved for FSGSBASE capability checks.
The application can then access it manually or using the getauxval()
function in newer glibc.
[ chang: Rebase and edit the changelog accordingly. ]
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
---
arch/x86/include/uapi/asm/hwcap2.h | 3 +++
arch/x86/kernel/cpu/common.c | 4 +++-
2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/uapi/asm/hwcap2.h b/arch/x86/include/uapi/asm/hwcap2.h
index 6ebaae90e207..c5ce54e749f6 100644
--- a/arch/x86/include/uapi/asm/hwcap2.h
+++ b/arch/x86/include/uapi/asm/hwcap2.h
@@ -5,4 +5,7 @@
/* MONITOR/MWAIT enabled in Ring 3 */
#define HWCAP2_RING3MWAIT (1 << 0)
+/* Kernel allows FSGSBASE instructions available in Ring 3 */
+#define HWCAP2_FSGSBASE BIT(1)
+
#endif
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3d7d4ca1a29e..3bdac91316c9 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1369,8 +1369,10 @@ static void identify_cpu(struct cpuinfo_x86 *c)
setup_umip(c);
/* Enable FSGSBASE instructions if available. */
- if (cpu_has(c, X86_FEATURE_FSGSBASE))
+ if (cpu_has(c, X86_FEATURE_FSGSBASE)) {
cr4_set_bits(X86_CR4_FSGSBASE);
+ elf_hwcap2 |= HWCAP2_FSGSBASE;
+ }
/*
* The vendor-specific functions might have changed features.
--
2.19.1
next prev parent reply other threads:[~2019-01-16 22:49 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-16 22:48 [PATCH v4 00/13] x86: Enable FSGSBASE instructions Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 01/13] taint: Introduce a new taint flag (insecure) Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 02/13] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 03/13] kbuild: Raise the minimum required binutils version to 2.21 Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 04/13] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions Chang S. Bae
2019-01-17 5:09 ` Andi Kleen
2019-01-17 18:04 ` Bae, Chang Seok
2019-01-16 22:48 ` [PATCH v4 05/13] x86/fsgsbase/64: Enable FSGSBASE instructions in the helper functions Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 06/13] x86/fsgsbase/64: Preserve FS/GS state in __switch_to() if FSGSBASE is on Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 07/13] x86/fsgsbase/64: When copying a thread, use the FSGSBASE instructions if available Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 08/13] x86/fsgsbase/64: Introduce the FIND_PERCPU_BASE macro Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 09/13] x86/fsgsbase/64: Use the per-CPU base as GSBASE at the paranoid_entry Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 10/13] selftests/x86/fsgsbase: Test WRGSBASE Chang S. Bae
2019-01-16 22:48 ` [PATCH v4 11/13] x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit Chang S. Bae
2019-01-16 22:48 ` Chang S. Bae [this message]
2019-01-16 22:48 ` [PATCH v4 13/13] x86/fsgsbase/64: Add documentation for FSGSBASE Chang S. Bae
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