diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2022-10-27 11:28:14 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-11-01 13:44:10 +0100 |
| commit | 931ab63664f02b17d2213ef36b83e1e50190a0aa (patch) | |
| tree | 9156c2db8252dfc019b5e8123de9f82419351503 /arch/x86/Kconfig | |
| parent | 9a479f766be1dd777e12e3e57b6ee4c3028a40a5 (diff) | |
x86/ibt: Implement FineIBT
Implement an alternative CFI scheme that merges both the fine-grained
nature of kCFI but also takes full advantage of the coarse grained
hardware CFI as provided by IBT.
To contrast:
kCFI is a pure software CFI scheme and relies on being able to read
text -- specifically the instruction *before* the target symbol, and
does the hash validation *before* doing the call (otherwise control
flow is compromised already).
FineIBT is a software and hardware hybrid scheme; by ensuring every
branch target starts with a hash validation it is possible to place
the hash validation after the branch. This has several advantages:
o the (hash) load is avoided; no memop; no RX requirement.
o IBT WAIT-FOR-ENDBR state is a speculation stop; by placing
the hash validation in the immediate instruction after
the branch target there is a minimal speculation window
and the whole is a viable defence against SpectreBHB.
o Kees feels obliged to mention it is slightly more vulnerable
when the attacker can write code.
Obviously this patch relies on kCFI, but additionally it also relies
on the padding from the call-depth-tracking patches. It uses this
padding to place the hash-validation while the call-sites are
re-written to modify the indirect target to be 16 bytes in front of
the original target, thus hitting this new preamble.
Notably, there is no hardware that needs call-depth-tracking (Skylake)
and supports IBT (Tigerlake and onwards).
Suggested-by: Joao Moreira (Intel) <joao@overdrivepizza.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20221027092842.634714496@infradead.org
Diffstat (limited to 'arch/x86/Kconfig')
| -rw-r--r-- | arch/x86/Kconfig | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 32818aa1dca4..479ee63898f5 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2463,17 +2463,27 @@ config FUNCTION_PADDING_BYTES default FUNCTION_PADDING_CFI if CFI_CLANG default FUNCTION_ALIGNMENT +config CALL_PADDING + def_bool n + depends on CC_HAS_ENTRY_PADDING && OBJTOOL + select FUNCTION_ALIGNMENT_16B + +config FINEIBT + def_bool y + depends on X86_KERNEL_IBT && CFI_CLANG && RETPOLINE + select CALL_PADDING + config HAVE_CALL_THUNKS def_bool y depends on CC_HAS_ENTRY_PADDING && RETHUNK && OBJTOOL config CALL_THUNKS def_bool n - select FUNCTION_ALIGNMENT_16B + select CALL_PADDING config PREFIX_SYMBOLS def_bool y - depends on CALL_THUNKS && !CFI_CLANG + depends on CALL_PADDING && !CFI_CLANG menuconfig SPECULATION_MITIGATIONS bool "Mitigations for speculative execution vulnerabilities" |