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c3f89986fd
This registers a breakpoint handler for the new breakpoint type (0x03) inserted by LLVM CLANG for CFI breakpoints. If we are in permissive mode, just print a backtrace and continue. Example with CONFIG_CFI_PERMISSIVE enabled: > echo CFI_FORWARD_PROTO > /sys/kernel/debug/provoke-crash/DIRECT lkdtm: Performing direct entry CFI_FORWARD_PROTO lkdtm: Calling matched prototype ... lkdtm: Calling mismatched prototype ... CFI failure at lkdtm_indirect_call+0x40/0x4c (target: 0x0; expected type: 0x00000000) WARNING: CPU: 1 PID: 112 at lkdtm_indirect_call+0x40/0x4c CPU: 1 PID: 112 Comm: sh Not tainted 6.8.0-rc1+ #150 Hardware name: ARM-Versatile Express (...) lkdtm: FAIL: survived mismatched prototype function call! lkdtm: Unexpected! This kernel (6.8.0-rc1+ armv7l) was built with CONFIG_CFI_CLANG=y As you can see the LKDTM test fails, but I expect that this would be expected behaviour in the permissive mode. We are currently not implementing target and type for the CFI breakpoint as this requires additional operand bundling compiler extensions. CPUs without breakpoint support cannot handle breakpoints naturally, in these cases the permissive mode will not work, CFI will fall over on an undefined instruction: Internal error: Oops - undefined instruction: 0 [#1] PREEMPT ARM CPU: 0 PID: 186 Comm: ash Tainted: G W 6.9.0-rc1+ #7 Hardware name: Gemini (Device Tree) PC is at lkdtm_indirect_call+0x38/0x4c LR is at lkdtm_CFI_FORWARD_PROTO+0x30/0x6c This is reasonable I think: it's the best CFI can do to ascertain the the control flow is not broken on these CPUs. Reviewed-by: Kees Cook <keescook@chromium.org> Tested-by: Kees Cook <keescook@chromium.org> Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> |
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