From 0e524e761fc2157f1037e0f5d616cd39e468d89c Mon Sep 17 00:00:00 2001 From: Matt Evans Date: Mon, 26 Mar 2018 17:55:21 +0100 Subject: [PATCH] powerpc: Clear branch trap (MSR.BE) before delivering SIGTRAP When using SIG_DBG_BRANCH_TRACING, MSR.BE is left enabled in the user context when single_step_exception() prepares the SIGTRAP delivery. The resulting branch-trap-within-the-SIGTRAP-handler isn't healthy. Commit 2538c2d08f46141550a1e68819efa8fe31c6e3dc broke this, by replacing an MSR mask operation of ~(MSR_SE | MSR_BE) with a call to clear_single_step() which only clears MSR_SE. This patch adds a new helper, clear_br_trace(), which clears the debug trap before invoking the signal handler. This helper is a NOP for BookE as SIG_DBG_BRANCH_TRACING isn't supported on BookE. Signed-off-by: Matt Evans Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/traps.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index 2c1a1d24f0ab..a2ef0c0e6c31 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c @@ -471,7 +471,7 @@ static inline int check_io_access(struct pt_regs *regs) /* single-step stuff */ #define single_stepping(regs) (current->thread.debug.dbcr0 & DBCR0_IC) #define clear_single_step(regs) (current->thread.debug.dbcr0 &= ~DBCR0_IC) - +#define clear_br_trace(regs) do {} while(0) #else /* On non-4xx, the reason for the machine check or program exception is in the MSR. */ @@ -484,6 +484,7 @@ static inline int check_io_access(struct pt_regs *regs) #define single_stepping(regs) ((regs)->msr & MSR_SE) #define clear_single_step(regs) ((regs)->msr &= ~MSR_SE) +#define clear_br_trace(regs) ((regs)->msr &= ~MSR_BE) #endif #if defined(CONFIG_E500) @@ -999,6 +1000,7 @@ void single_step_exception(struct pt_regs *regs) enum ctx_state prev_state = exception_enter(); clear_single_step(regs); + clear_br_trace(regs); if (kprobe_post_handler(regs)) return; -- 2.11.0