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Message-Id: <20160628162522.ee8ec57e686d8dc80c265211@kernel.org> Date: Tue, 28 Jun 2016 16:25:22 +0900 From: Masami Hiramatsu <mhiramat@...nel.org> To: David Long <dave.long@...aro.org> Cc: Pratyush Anand <panand@...hat.com>, Mark Brown <broonie@...nel.org>, Catalin Marinas <catalin.marinas@....com>, Huang Shijie <shijie.huang@....com>, James Morse <james.morse@....com>, Marc Zyngier <marc.zyngier@....com>, Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>, Will Deacon <will.deacon@....com>, William Cohen <wcohen@...hat.com>, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Steve Capper <steve.capper@...aro.org>, Li Bin <huawei.libin@...wei.com>, Adam Buchbinder <adam.buchbinder@...il.com>, Alex Bennée <alex.bennee@...aro.org>, Andrew Morton <akpm@...ux-foundation.org>, Andrey Ryabinin <ryabinin.a.a@...il.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Christoffer Dall <christoffer.dall@...aro.org>, Daniel Thompson <daniel.thompson@...aro.org>, Dave P Martin <Dave.Martin@....com>, Jens Wiklander <jens.wiklander@...aro.org>, Jisheng Zhang <jszhang@...vell.com>, John Blackwood <john.blackwood@...r.com>, Mark Rutland <mark.rutland@....com>, Petr Mladek <pmladek@...e.com>, Robin Murphy <robin.murphy@....com>, Suzuki K Poulose <suzuki.poulose@....com>, Vladimir Murzin <Vladimir.Murzin@....com>, Yang Shi <yang.shi@...aro.org>, Zi Shen Lim <zlim.lnx@...il.com>, yalin wang <yalin.wang2010@...il.com> Subject: Re: [PATCH v14 04/10] arm64: Kprobes with single stepping support On Mon, 27 Jun 2016 10:06:57 -0400 David Long <dave.long@...aro.org> wrote: > 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 <sandeepa.s.prabhu@...il.com> > >> > >> 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 <sandeepa.s.prabhu@...il.com> > >> Signed-off-by: David A. Long <dave.long@...aro.org> > >> Signed-off-by: Pratyush Anand <panand@...hat.com> > >> --- > >> 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. Yeah, if you've already been sure it will be done, I'm OK to rename it "probe" :) I just didn't know your work. > > > > >> 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. Ah, right. we have something similar routines in asm-generic/ptrace.h. Feel free to include it. Thanks, > > > > https://github.com/pratyushanand/linux/commit/bb3e114797c2888ed8ad528cca20e569dd2d818e > > I will look at this. > > > > > ~Pratyush > > > > Thanks, > -dl > -- Masami Hiramatsu <mhiramat@...nel.org>
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