From 0c4519e825c9e2b6a8310deff8582f8c35bfbba9 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 24 Jun 2010 21:21:27 +0200 Subject: [PATCH] x86: Set resume bit before returning from breakpoint exception Instruction breakpoints trigger before the instruction executes, and returning back from the breakpoint handler brings us again to the instruction that breakpointed. This naturally bring to a breakpoint recursion. To solve this, x86 has the Resume Bit trick. When the cpu flags have the RF flag set, the next instruction won't trigger any instruction breakpoint, and once this instruction is executed, RF is cleared back. This let's us jump back to the instruction that triggered the breakpoint without recursion. Use this when an instruction breakpoint triggers. Signed-off-by: Frederic Weisbecker Cc: Will Deacon Cc: Prasad Cc: Mahesh Salgaonkar Cc: Paul Mackerras Cc: Ingo Molnar Cc: Jason Wessel --- arch/x86/kernel/hw_breakpoint.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index a8f1b80..eaa6ae2 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -466,6 +466,13 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args) perf_bp_event(bp, args->regs); + /* + * Set up resume flag to avoid breakpoint recursion when + * returning back to origin. + */ + if (bp->hw.info.type == X86_BREAKPOINT_EXECUTE) + args->regs->flags |= X86_EFLAGS_RF; + rcu_read_unlock(); } /* -- 2.7.4