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author | Waiman Long <longman@redhat.com> | 2019-01-16 17:01:36 -0500 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2019-01-29 22:11:49 +0100 |
commit | 71368af9027f18fe5d1c6f372cfdff7e4bde8b48 (patch) | |
tree | 71666188c5b97195fa4114674fa6e84471b2b460 /arch/x86/kernel/process.c | |
parent | 4aa9fc2a435abe95a1e8d7f8c7b3d6356514b37a (diff) | |
download | linux-stable-71368af9027f18fe5d1c6f372cfdff7e4bde8b48.tar.gz linux-stable-71368af9027f18fe5d1c6f372cfdff7e4bde8b48.tar.bz2 linux-stable-71368af9027f18fe5d1c6f372cfdff7e4bde8b48.zip |
x86/speculation: Add PR_SPEC_DISABLE_NOEXEC
With the default SPEC_STORE_BYPASS_SECCOMP/SPEC_STORE_BYPASS_PRCTL mode,
the TIF_SSBD bit will be inherited when a new task is fork'ed or cloned.
It will also remain when a new program is execve'ed.
Only certain class of applications (like Java) that can run on behalf of
multiple users on a single thread will require disabling speculative store
bypass for security purposes. Those applications will call prctl(2) at
startup time to disable SSB. They won't rely on the fact the SSB might have
been disabled. Other applications that don't need SSBD will just move on
without checking if SSBD has been turned on or not.
The fact that the TIF_SSBD is inherited across execve(2) boundary will
cause performance of applications that don't need SSBD but their
predecessors have SSBD on to be unwittingly impacted especially if they
write to memory a lot.
To remedy this problem, a new PR_SPEC_DISABLE_NOEXEC argument for the
PR_SET_SPECULATION_CTRL option of prctl(2) is added to allow applications
to specify that the SSBD feature bit on the task structure should be
cleared whenever a new program is being execve'ed.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: KarimAllah Ahmed <karahmed@amazon.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Link: https://lkml.kernel.org/r/1547676096-3281-1-git-send-email-longman@redhat.com
Diffstat (limited to 'arch/x86/kernel/process.c')
-rw-r--r-- | arch/x86/kernel/process.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 90ae0ca51083..58ac7be52c7a 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -255,6 +255,18 @@ void arch_setup_new_exec(void) /* If cpuid was previously disabled for this task, re-enable it. */ if (test_thread_flag(TIF_NOCPUID)) enable_cpuid(); + + /* + * Don't inherit TIF_SSBD across exec boundary when + * PR_SPEC_DISABLE_NOEXEC is used. + */ + if (test_thread_flag(TIF_SSBD) && + task_spec_ssb_noexec(current)) { + clear_thread_flag(TIF_SSBD); + task_clear_spec_ssb_disable(current); + task_clear_spec_ssb_noexec(current); + speculation_ctrl_update(task_thread_info(current)->flags); + } } static inline void switch_to_bitmap(struct thread_struct *prev, |