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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 2538c2d08f 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 <matt@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Matt Evans 2018-03-26 17:55:21 +01:00 committed by Michael Ellerman
parent 4b7e5532d2
commit 0e524e761f
1 changed files with 3 additions and 1 deletions
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4
arch/powerpc/kernel/traps.c
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@ -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;