diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2022-09-15 13:11:23 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-10-17 16:41:13 +0200 |
| commit | e81dc127ef69887c72735a3e3868930e2bf313ed (patch) | |
| tree | ab2f1fd791dba8e3d3db75b441b962ab2dc2cb5a /arch/x86/Kconfig | |
| parent | 239f2e248ef12840178a3ed1a217f19b5fbfde26 (diff) | |
x86/callthunks: Add call patching for call depth tracking
Mitigating the Intel SKL RSB underflow issue in software requires to
track the call depth. That is every CALL and every RET need to be
intercepted and additional code injected.
The existing retbleed mitigations already include means of redirecting
RET to __x86_return_thunk; this can be re-purposed and RET can be
redirected to another function doing RET accounting.
CALL accounting will use the function padding introduced in prior
patches. For each CALL instruction, the destination symbol's padding
is rewritten to do the accounting and the CALL instruction is adjusted
to call into the padding.
This ensures only affected CPUs pay the overhead of this accounting.
Unaffected CPUs will leave the padding unused and have their 'JMP
__x86_return_thunk' replaced with an actual 'RET' instruction.
Objtool has been modified to supply a .call_sites section that lists
all the 'CALL' instructions. Additionally the paravirt instruction
sites are iterated since they will have been patched from an indirect
call to direct calls (or direct instructions in which case it'll be
ignored).
Module handling and the actual thunk code for SKL will be added in
subsequent steps.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111147.470877038@infradead.org
Diffstat (limited to 'arch/x86/Kconfig')
| -rw-r--r-- | arch/x86/Kconfig | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 6ae7fa4b8eb7..a1dae9d5e3da 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2541,6 +2541,18 @@ config CALL_DEPTH_TRACKING is unused. On affected SKL systems this results in a significant performance gain over the IBRS mitigation. +config CALL_THUNKS_DEBUG + bool "Enable call thunks and call depth tracking debugging" + depends on CALL_DEPTH_TRACKING + select FUNCTION_ALIGNMENT_32B + default n + help + Enable call/ret counters for imbalance detection and build in + a noisy dmesg about callthunks generation and call patching for + trouble shooting. The debug prints need to be enabled on the + kernel command line with 'debug-callthunks'. + Only enable this, when you are debugging call thunks as this + creates a noticable runtime overhead. If unsure say N. config CPU_IBPB_ENTRY bool "Enable IBPB on kernel entry" |