From ddc9863e9e9025e2fc0c8dba31cc060cd626606f Mon Sep 17 00:00:00 2001 From: Sami Tolvanen Date: Mon, 27 Apr 2020 09:00:10 -0700 Subject: [PATCH] scs: Disable when function graph tracing is enabled The graph tracer hooks returns by modifying frame records on the (regular) stack, but with SCS the return address is taken from the shadow stack, and the value in the frame record has no effect. As we don't currently have a mechanism to determine the corresponding slot on the shadow stack (and to pass this through the ftrace infrastructure), for now let's disable SCS when the graph tracer is enabled. With SCS the return address is taken from the shadow stack and the value in the frame record has no effect. The mcount based graph tracer hooks returns by modifying frame records on the (regular) stack, and thus is not compatible. The patchable-function-entry graph tracer used for DYNAMIC_FTRACE_WITH_REGS modifies the LR before it is saved to the shadow stack, and is compatible. Modifying the mcount based graph tracer to work with SCS would require a mechanism to determine the corresponding slot on the shadow stack (and to pass this through the ftrace infrastructure), and we expect that everyone will eventually move to the patchable-function-entry based graph tracer anyway, so for now let's disable SCS when the mcount-based graph tracer is enabled. SCS and patchable-function-entry are both supported from LLVM 10.x. Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Reviewed-by: Mark Rutland Signed-off-by: Will Deacon --- arch/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/Kconfig b/arch/Kconfig index 334a3d9b19df..45dfca9a98d3 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -543,6 +543,7 @@ config ARCH_SUPPORTS_SHADOW_CALL_STACK config SHADOW_CALL_STACK bool "Clang Shadow Call Stack" depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK + depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER help This option enables Clang's Shadow Call Stack, which uses a shadow stack to protect function return addresses from being -- GitLab