From mboxrd@z Thu Jan 1 00:00:00 1970 From: dave.long@linaro.org (David Long) Date: Mon, 27 Jun 2016 10:06:57 -0400 Subject: [PATCH v14 04/10] arm64: Kprobes with single stepping support In-Reply-To: <20160627065749.GB29870@dhcppc9> References: <1466996813-23295-1-git-send-email-dave.long@linaro.org> <1466996813-23295-5-git-send-email-dave.long@linaro.org> <20160627065749.GB29870@dhcppc9> Message-ID: <57713301.2020706@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 06/27/2016 02:57 AM, Pratyush Anand wrote: > Hi David, > > On 26/06/2016:11:06:47 PM, David Long wrote: >> From: Sandeepa Prabhu >> >> Add support for basic kernel probes(kprobes) and jump probes >> (jprobes) for ARM64. >> >> Kprobes utilizes software breakpoint and single step debug >> exceptions supported on ARM v8. >> >> A software breakpoint is placed at the probe address to trap the >> kernel execution into the kprobe handler. >> >> ARM v8 supports enabling single stepping before the break exception >> return (ERET), with next PC in exception return address (ELR_EL1). The >> kprobe handler prepares an executable memory slot for out-of-line >> execution with a copy of the original instruction being probed, and >> enables single stepping. The PC is set to the out-of-line slot address >> before the ERET. With this scheme, the instruction is executed with the >> exact same register context except for the PC (and DAIF) registers. >> >> Debug mask (PSTATE.D) is enabled only when single stepping a recursive >> kprobe, e.g.: during kprobes reenter so that probed instruction can be >> single stepped within the kprobe handler -exception- context. >> The recursion depth of kprobe is always 2, i.e. upon probe re-entry, >> any further re-entry is prevented by not calling handlers and the case >> counted as a missed kprobe). >> >> Single stepping from the x-o-l slot has a drawback for PC-relative accesses >> like branching and symbolic literals access as the offset from the new PC >> (slot address) may not be ensured to fit in the immediate value of >> the opcode. Such instructions need simulation, so reject >> probing them. >> >> Instructions generating exceptions or cpu mode change are rejected >> for probing. >> >> Exclusive load/store instructions are rejected too. Additionally, the >> code is checked to see if it is inside an exclusive load/store sequence >> (code from Pratyush). >> >> System instructions are mostly enabled for stepping, except MSR/MRS >> accesses to "DAIF" flags in PSTATE, which are not safe for >> probing. >> >> Thanks to Steve Capper and Pratyush Anand for several suggested >> Changes. >> >> Signed-off-by: Sandeepa Prabhu >> Signed-off-by: David A. Long >> Signed-off-by: Pratyush Anand >> --- >> arch/arm64/Kconfig | 1 + >> arch/arm64/include/asm/debug-monitors.h | 5 + >> arch/arm64/include/asm/insn.h | 2 + >> arch/arm64/include/asm/kprobes.h | 60 ++++ >> arch/arm64/include/asm/probes.h | 34 +++ >> arch/arm64/include/asm/ptrace.h | 1 + >> arch/arm64/kernel/Makefile | 2 +- >> arch/arm64/kernel/debug-monitors.c | 16 +- >> arch/arm64/kernel/kprobes/Makefile | 1 + >> arch/arm64/kernel/kprobes/decode-insn.c | 143 +++++++++ >> arch/arm64/kernel/kprobes/decode-insn.h | 34 +++ >> arch/arm64/kernel/kprobes/kprobes.c | 525 ++++++++++++++++++++++++++++++++ >> arch/arm64/kernel/vmlinux.lds.S | 1 + >> arch/arm64/mm/fault.c | 26 ++ >> 14 files changed, 848 insertions(+), 3 deletions(-) >> create mode 100644 arch/arm64/include/asm/kprobes.h >> create mode 100644 arch/arm64/include/asm/probes.h >> create mode 100644 arch/arm64/kernel/kprobes/Makefile >> create mode 100644 arch/arm64/kernel/kprobes/decode-insn.c >> create mode 100644 arch/arm64/kernel/kprobes/decode-insn.h > > Can we rename kernel/kprobes as kernel/probes? uprobes code will use > decode-insn.c and further simulate-insn.c as well. So, I would like to place my > uprobes.c in same directory. I had some reservations about making it a "kprobes" subdir for that reason but the advice I got was to simply go with Masami Hiramatsu's specific feedback and have a subsequent uprobes patch move these files to a replacement "probes" subdir. If there ends up being yet another revision of this patch maybe he will consider allowing it to be called "probes" from the start. > >> create mode 100644 arch/arm64/kernel/kprobes/kprobes.c >> > > [...] > >> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h >> index 6c0c7d3..c7bbeed 100644 >> --- a/arch/arm64/include/asm/ptrace.h >> +++ b/arch/arm64/include/asm/ptrace.h >> @@ -209,6 +209,7 @@ struct task_struct; >> int valid_user_regs(struct user_pt_regs *regs, struct task_struct *task); >> >> #define instruction_pointer(regs) ((unsigned long)(regs)->pc) >> +#define instruction_pointer_set(regs, value) ((regs)->pc = ((u64) (value))) > > IIRC, Will Daecon had asked to include asm-generic/ptrace.h into asm/ptrace.h when > I had done similar changes for uprobe needs. May be you can pick patch from > my uprobe tree. > > https://github.com/pratyushanand/linux/commit/bb3e114797c2888ed8ad528cca20e569dd2d818e I will look at this. > > ~Pratyush > Thanks, -dl