From: Sasha Levin <sashal@kernel.org>
To: tglx@linutronix.de, luto@kernel.org, ak@linux.intel.com
Cc: corbet@lwn.net, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
shuah@kernel.org, gregkh@linuxfoundation.org,
tony.luck@intel.com, chang.seok.bae@intel.com,
dave.hansen@linux.intel.com, peterz@infradead.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
jarkko.sakkinen@linux.intel.com,
"H . Peter Anvin" <hpa@zytor.com>,
Dave Hansen <dave.hansen@intel.com>,
Sasha Levin <sashal@kernel.org>
Subject: [PATCH v13 08/16] x86/speculation/swapgs: Check FSGSBASE in enabling SWAPGS mitigation
Date: Thu, 28 May 2020 16:13:54 -0400 [thread overview]
Message-ID: <20200528201402.1708239-9-sashal@kernel.org> (raw)
In-Reply-To: <20200528201402.1708239-1-sashal@kernel.org>
From: Tony Luck <tony.luck@intel.com>
Before enabling FSGSBASE the kernel could safely assume that the content
of GS base was a user address. Thus any speculative access as the result
of a mispredicted branch controlling the execution of SWAPGS would be to
a user address. So systems with speculation-proof SMAP did not need to
add additional LFENCE instructions to mitigate.
With FSGSBASE enabled a hostile user can set GS base to a kernel address.
So they can make the kernel speculatively access data they wish to leak
via a side channel. This means that SMAP provides no protection.
Add FSGSBASE as an additional condition to enable the fence-based SWAPGS
mitigation.
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kernel/cpu/bugs.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ed54b3b21c39..487603ea51cd 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -450,14 +450,12 @@ static void __init spectre_v1_select_mitigation(void)
* If FSGSBASE is enabled, the user can put a kernel address in
* GS, in which case SMAP provides no protection.
*
- * [ NOTE: Don't check for X86_FEATURE_FSGSBASE until the
- * FSGSBASE enablement patches have been merged. ]
- *
* If FSGSBASE is disabled, the user can only put a user space
* address in GS. That makes an attack harder, but still
* possible if there's no SMAP protection.
*/
- if (!smap_works_speculatively()) {
+ if (boot_cpu_has(X86_FEATURE_FSGSBASE) ||
+ !smap_works_speculatively()) {
/*
* Mitigation can be provided from SWAPGS itself or
* PTI as the CR3 write in the Meltdown mitigation
--
2.25.1
next prev parent reply other threads:[~2020-05-28 20:14 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 20:13 [PATCH v13 00/16] Enable FSGSBASE instructions Sasha Levin
2020-05-28 20:13 ` [PATCH v13 01/16] x86/ptrace: Prevent ptrace from clearing the FS/GS selector Sasha Levin
2020-05-28 20:13 ` [PATCH v13 02/16] x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Sasha Levin
2020-05-28 20:13 ` [PATCH v13 03/16] x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions Sasha Levin
2020-05-28 20:13 ` [PATCH v13 04/16] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions Sasha Levin
2020-05-28 20:13 ` [PATCH v13 05/16] x86/process/64: Use FSBSBASE in switch_to() if available Sasha Levin
2020-05-28 20:13 ` [PATCH v13 06/16] x86/process/64: Make save_fsgs() public available Sasha Levin
2020-06-18 13:50 ` [tip: x86/fsgsbase] x86/process/64: Make save_fsgs_for_kvm() ready for FSGSBASE tip-bot2 for Thomas Gleixner
2020-05-28 20:13 ` [PATCH v13 07/16] x86/process/64: Use FSGSBASE instructions on thread copy and ptrace Sasha Levin
2020-05-28 20:13 ` Sasha Levin [this message]
2020-06-18 13:50 ` [tip: x86/fsgsbase] x86/speculation/swapgs: Check FSGSBASE in enabling SWAPGS mitigation tip-bot2 for Tony Luck
2020-05-28 20:13 ` [PATCH v13 09/16] x86/entry/64: Switch CR3 before SWAPGS in paranoid entry Sasha Levin
2020-05-28 20:13 ` [PATCH v13 10/16] x86/entry/64: Introduce the FIND_PERCPU_BASE macro Sasha Levin
2020-05-28 20:13 ` [PATCH v13 11/16] x86/entry/64: Handle FSGSBASE enabled paranoid entry/exit Sasha Levin
2020-05-28 20:13 ` [PATCH v13 12/16] x86/cpu: Enable FSGSBASE on 64bit by default and add a chicken bit Sasha Levin
2020-05-28 20:13 ` [PATCH v13 13/16] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Sasha Levin
2020-10-26 17:18 ` [PATCH] x86/elf: Fix use of internal macro BIT in uapi header Thiago Macieira
2020-05-28 20:14 ` [PATCH v13 14/16] Documentation/x86/64: Add documentation for GS/FS addressing mode Sasha Levin
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Thomas Gleixner
2020-05-28 20:14 ` [PATCH v13 15/16] selftests/x86/fsgsbase: Test GS selector on ptracer-induced GS base write Sasha Levin
2020-05-29 14:40 ` Shuah Khan
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Chang S. Bae
2020-05-28 20:14 ` [PATCH v13 16/16] selftests/x86/fsgsbase: Test ptracer-induced GS base write with FSGSBASE Sasha Levin
2020-05-29 14:42 ` Shuah Khan
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Chang S. Bae
2020-06-18 14:18 ` [PATCH v13 00/16] Enable FSGSBASE instructions Thomas Gleixner
2020-06-18 18:08 ` Andy Lutomirski
2020-06-18 18:25 ` Thomas Gleixner
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