Re: [PATCH v8 04/12] scs: disable when function graph tracing is enabled
From: Mark Rutland <mark.rutland@arm.com>
Date: 2020-02-19 11:34:06
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On Tue, Feb 18, 2020 at 04:08:09PM -0800, Sami Tolvanen wrote:
quoted hunk ↗ jump to hunk
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. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <redacted> --- arch/Kconfig | 1 + 1 file changed, 1 insertion(+)diff --git a/arch/Kconfig b/arch/Kconfig index 66b34fd0df54..4102b8e0eea9 100644 --- a/arch/Kconfig +++ b/arch/Kconfig@@ -535,6 +535,7 @@ config ARCH_SUPPORTS_SHADOW_CALL_STACK config SHADOW_CALL_STACK bool "Clang Shadow Call Stack" + depends on !FUNCTION_GRAPH_TRACER
Fangrui Song has implemented `-fpatchable-function-entry` in LLVM (for 10.x onwards), so we can support this when DYNAMIC_FTRACE_WITH_REGS is selected. This can be: depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER ... and we can update the commit message to something like: | 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. Assuming you're happy with that: Reviewed-by: Mark Rutland <mark.rutland@arm.com> Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel