From 0c4519e825c9e2b6a8310deff8582f8c35bfbba9 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 24 Jun 2010 21:21:27 +0200 Subject: 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(+) (limited to 'arch/x86/kernel/hw_breakpoint.c') diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index a8f1b803d2fd..eaa6ae2a010b 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(); } /* -- cgit v1.2.3 From f7809daf64bf119fef70af172db6a0636fa51f92 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 24 Jun 2010 10:00:24 +0200 Subject: x86: Support for instruction breakpoints Instruction breakpoints need to have a specific length of 0 to be working. Bring this support but also take care the user is not trying to set an unsupported length, like a range breakpoint for example. Signed-off-by: Frederic Weisbecker Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Arnaldo Carvalho de Melo Cc: Paul Mackerras Cc: Prasad Cc: Mahesh Salgaonkar Cc: Will Deacon Cc: Jason Wessel --- arch/x86/include/asm/hw_breakpoint.h | 2 +- arch/x86/kernel/hw_breakpoint.c | 44 ++++++++++++++++++++++++------------ 2 files changed, 30 insertions(+), 16 deletions(-) (limited to 'arch/x86/kernel/hw_breakpoint.c') diff --git a/arch/x86/include/asm/hw_breakpoint.h b/arch/x86/include/asm/hw_breakpoint.h index 942255310e6a..528a11e8d3e3 100644 --- a/arch/x86/include/asm/hw_breakpoint.h +++ b/arch/x86/include/asm/hw_breakpoint.h @@ -20,10 +20,10 @@ struct arch_hw_breakpoint { #include /* Available HW breakpoint length encodings */ +#define X86_BREAKPOINT_LEN_X 0x00 #define X86_BREAKPOINT_LEN_1 0x40 #define X86_BREAKPOINT_LEN_2 0x44 #define X86_BREAKPOINT_LEN_4 0x4c -#define X86_BREAKPOINT_LEN_EXECUTE 0x40 #ifdef CONFIG_X86_64 #define X86_BREAKPOINT_LEN_8 0x48 diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index eaa6ae2a010b..a474ec37c32f 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -208,6 +208,9 @@ int arch_bp_generic_fields(int x86_len, int x86_type, { /* Len */ switch (x86_len) { + case X86_BREAKPOINT_LEN_X: + *gen_len = sizeof(long); + break; case X86_BREAKPOINT_LEN_1: *gen_len = HW_BREAKPOINT_LEN_1; break; @@ -251,6 +254,29 @@ static int arch_build_bp_info(struct perf_event *bp) info->address = bp->attr.bp_addr; + /* Type */ + switch (bp->attr.bp_type) { + case HW_BREAKPOINT_W: + info->type = X86_BREAKPOINT_WRITE; + break; + case HW_BREAKPOINT_W | HW_BREAKPOINT_R: + info->type = X86_BREAKPOINT_RW; + break; + case HW_BREAKPOINT_X: + info->type = X86_BREAKPOINT_EXECUTE; + /* + * x86 inst breakpoints need to have a specific undefined len. + * But we still need to check userspace is not trying to setup + * an unsupported length, to get a range breakpoint for example. + */ + if (bp->attr.bp_len == sizeof(long)) { + info->len = X86_BREAKPOINT_LEN_X; + return 0; + } + default: + return -EINVAL; + } + /* Len */ switch (bp->attr.bp_len) { case HW_BREAKPOINT_LEN_1: @@ -271,21 +297,6 @@ static int arch_build_bp_info(struct perf_event *bp) return -EINVAL; } - /* Type */ - switch (bp->attr.bp_type) { - case HW_BREAKPOINT_W: - info->type = X86_BREAKPOINT_WRITE; - break; - case HW_BREAKPOINT_W | HW_BREAKPOINT_R: - info->type = X86_BREAKPOINT_RW; - break; - case HW_BREAKPOINT_X: - info->type = X86_BREAKPOINT_EXECUTE; - break; - default: - return -EINVAL; - } - return 0; } /* @@ -305,6 +316,9 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp) ret = -EINVAL; switch (info->len) { + case X86_BREAKPOINT_LEN_X: + align = sizeof(long) -1; + break; case X86_BREAKPOINT_LEN_1: align = 0; break; -- cgit v1.2.3