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authorThomas Gleixner <tglx@linutronix.de>2018-04-29 15:26:40 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-05-22 16:58:01 +0200
commita078e3e81964c31079627dd32c3ea714d5b1531e (patch)
tree211b57cbf1f0300f43b780463344f91b7f652f43 /Documentation
parent89c6e9b599c573802de1b2fff6a9ccd99c3c4e57 (diff)
x86/speculation: Add prctl for Speculative Store Bypass mitigation
commit a73ec77ee17ec556fe7f165d00314cb7c047b1ac upstream Add prctl based control for Speculative Store Bypass mitigation and make it the default mitigation for Intel and AMD. Andi Kleen provided the following rationale (slightly redacted): There are multiple levels of impact of Speculative Store Bypass: 1) JITed sandbox. It cannot invoke system calls, but can do PRIME+PROBE and may have call interfaces to other code 2) Native code process. No protection inside the process at this level. 3) Kernel. 4) Between processes. The prctl tries to protect against case (1) doing attacks. If the untrusted code can do random system calls then control is already lost in a much worse way. So there needs to be system call protection in some way (using a JIT not allowing them or seccomp). Or rather if the process can subvert its environment somehow to do the prctl it can already execute arbitrary code, which is much worse than SSB. To put it differently, the point of the prctl is to not allow JITed code to read data it shouldn't read from its JITed sandbox. If it already has escaped its sandbox then it can already read everything it wants in its address space, and do much worse. The ability to control Speculative Store Bypass allows to enable the protection selectively without affecting overall system performance. Based on an initial patch from Tim Chen. Completely rewritten. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/kernel-parameters.txt6
1 files changed, 5 insertions, 1 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 792ac917411a..543923b35260 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -4001,7 +4001,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
off - Unconditionally enable Speculative Store Bypass
auto - Kernel detects whether the CPU model contains an
implementation of Speculative Store Bypass and
- picks the most appropriate mitigation
+ picks the most appropriate mitigation.
+ prctl - Control Speculative Store Bypass per thread
+ via prctl. Speculative Store Bypass is enabled
+ for a process by default. The state of the control
+ is inherited on fork.
Not specifying this option is equivalent to
spec_store_bypass_disable=auto.