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| author |   Thomas Gleixner <tglx@linutronix.de> | 2018-04-29 15:26:40 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2018-05-03 13:55:51 +0200 |
| commit | a73ec77ee17ec556fe7f165d00314cb7c047b1ac (patch) | |
| tree | fc626ec0298a4d788dbd8705aacfdce3e3e68bcc /Documentation | |
| parent | x86/process: Allow runtime control of Speculative Store Bypass (diff) | |
| download | linux-dev-a73ec77ee17ec556fe7f165d00314cb7c047b1ac.tar.xz linux-dev-a73ec77ee17ec556fe7f165d00314cb7c047b1ac.zip | |
x86/speculation: Add prctl for Speculative Store Bypass mitigation
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>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f32112c55f7e..a8d2ae1e335b 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4053,7 +4053,11 @@ 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. |