From 2d21889f8b5c50f65f5162bc972b0b1626b97be2 Mon Sep 17 00:00:00 2001 From: Jean-Philippe Brucker Date: Wed, 24 Jun 2020 13:22:54 +0200 Subject: [PATCH] arm64: Don't insert a BTI instruction at inner labels Some ftrace features are broken since commit 714a8d02ca4d ("arm64: asm: Override SYM_FUNC_START when building the kernel with BTI"). For example the function_graph tracer: $ echo function_graph > /sys/kernel/debug/tracing/current_tracer [ 36.107016] WARNING: CPU: 0 PID: 115 at kernel/trace/ftrace.c:2691 ftrace_modify_all_code+0xc8/0x14c When ftrace_modify_graph_caller() attempts to write a branch at ftrace_graph_call, it finds the "BTI J" instruction inserted by SYM_INNER_LABEL() instead of a NOP, and aborts. It turns out we don't currently need the BTI landing pads inserted by SYM_INNER_LABEL: * ftrace_call and ftrace_graph_call are only used for runtime patching of the active tracer. The patched code is not reached from a branch. * install_el2_stub is reached from a CBZ instruction, which doesn't change PSTATE.BTYPE. * __guest_exit is reached from B instructions in the hyp-entry vectors, which aren't subject to BTI checks either. Remove the BTI annotation from SYM_INNER_LABEL. Fixes: 714a8d02ca4d ("arm64: asm: Override SYM_FUNC_START when building the kernel with BTI") Signed-off-by: Jean-Philippe Brucker Reviewed-by: Mark Brown Link: https://lore.kernel.org/r/20200624112253.1602786-1-jean-philippe@linaro.org Signed-off-by: Will Deacon --- arch/arm64/include/asm/linkage.h | 6 ------ 1 file changed, 6 deletions(-) diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h index 81fefd2..ba89a9a 100644 --- a/arch/arm64/include/asm/linkage.h +++ b/arch/arm64/include/asm/linkage.h @@ -12,7 +12,6 @@ * instead. */ #define BTI_C hint 34 ; -#define BTI_J hint 36 ; /* * When using in-kernel BTI we need to ensure that PCS-conformant assembly @@ -43,11 +42,6 @@ SYM_START(name, SYM_L_WEAK, SYM_A_NONE) \ BTI_C -#define SYM_INNER_LABEL(name, linkage) \ - .type name SYM_T_NONE ASM_NL \ - SYM_ENTRY(name, linkage, SYM_A_NONE) \ - BTI_J - #endif /* -- 2.7.4