On Mon, 24 Jul 2017 14:28:36 +0000 (UTC) Mathieu Desnoyers <mathieu.desnoy...@efficios.com> wrote:
> ----- On Jul 24, 2017, at 9:50 AM, Masami Hiramatsu mhira...@kernel.org wrote: > > > Since the kernel segment registers are not prepared at the > > entry of irq-entry code, if a kprobe on such code is > > jump-optimized, accessing per-cpu variables may cause > > kernel panic. > > However, if the kprobe is not optimized, it kicks int3 > > exception and set segment registers correctly. > > > > This checks probe-address and if it is in irq-entry code, > > it prohibits optimizing such kprobes. This means we can > > continuously probing such interrupt handlers by kprobes > > but it is not optimized anymore. > > > > Signed-off-by: Masami Hiramatsu <mhira...@kernel.org> > > Reported-by: Francis Deslauriers <francis.deslauri...@efficios.com> > > Tested-by: Francis Deslauriers <francis.deslauri...@efficios.com> > > --- > > arch/x86/entry/entry_64.S | 2 +- > > arch/x86/include/asm/unwind.h | 1 + > > arch/x86/kernel/kprobes/opt.c | 4 ++-- > > arch/x86/kernel/unwind_frame.c | 4 ++-- > > 4 files changed, 6 insertions(+), 5 deletions(-) > > > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > > index aa58155..9652c34 100644 > > --- a/arch/x86/entry/entry_64.S > > +++ b/arch/x86/entry/entry_64.S > > @@ -766,7 +766,7 @@ apicinterrupt3 \num trace(\sym) smp_trace(\sym) > > #endif > > > > /* Make sure APIC interrupt handlers end up in the irqentry section: */ > > -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) > > +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || > > defined(CONFIG_KPROBES) > > # define PUSH_SECTION_IRQENTRY .pushsection .irqentry.text, "ax" > > # define POP_SECTION_IRQENTRY .popsection > > #else > > diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h > > index e667649..a9896fb9 100644 > > --- a/arch/x86/include/asm/unwind.h > > +++ b/arch/x86/include/asm/unwind.h > > @@ -28,6 +28,7 @@ void __unwind_start(struct unwind_state *state, struct > > task_struct *task, > > bool unwind_next_frame(struct unwind_state *state); > > > > unsigned long unwind_get_return_address(struct unwind_state *state); > > +bool in_entry_code(unsigned long ip); > > > > static inline bool unwind_done(struct unwind_state *state) > > { > > diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c > > index 69ea0bc..a51c144 100644 > > --- a/arch/x86/kernel/kprobes/opt.c > > +++ b/arch/x86/kernel/kprobes/opt.c > > @@ -39,6 +39,7 @@ > > #include <asm/insn.h> > > #include <asm/debugreg.h> > > #include <asm/set_memory.h> > > +#include <asm/unwind.h> > > > > #include "common.h" > > > > @@ -253,8 +254,7 @@ static int can_optimize(unsigned long paddr) > > * Do not optimize in the entry code due to the unstable > > * stack handling. > > */ > > - if ((paddr >= (unsigned long)__entry_text_start) && > > - (paddr < (unsigned long)__entry_text_end)) > > + if (in_entry_code(paddr)) > > return 0; > > > > /* Check there is enough space for a relative jump. */ > > diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c > > index b9389d7..95123ce 100644 > > --- a/arch/x86/kernel/unwind_frame.c > > +++ b/arch/x86/kernel/unwind_frame.c > > @@ -84,14 +84,14 @@ static size_t regs_size(struct pt_regs *regs) > > return sizeof(*regs); > > } > > > > -static bool in_entry_code(unsigned long ip) > > +bool in_entry_code(unsigned long ip) > > { > > char *addr = (char *)ip; > > > > if (addr >= __entry_text_start && addr < __entry_text_end) > > return true; > > > > -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) > > +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || > > defined(CONFIG_KPROBES) > > Hi Masami, > > With this patch applied on top of v4.12.3, I can generate a configuration > with CONFIG_KPROBES=y and CONFIG_FRAME_POINTER=n, which leads to: > > arch/x86/built-in.o: In function `can_optimize': > /home/efficios/git/linux/arch/x86/kernel/kprobes/opt.c:250: undefined > reference to `in_entry_code' > > (see attached .config) Oops, right. > arch/x86/kernel/unwind_frame.c is only compiled when CONFIG_FRAME_POINTER > is enabled, but CONFIG_KPROBES does not depend on it. > > Is unwind_frame.c really where in_entry_code() should be implemented, now > that its symbol becomes exposed to other compile units ? At least kprobes needs it. (as far It seems we can move it in arch/x86/entry/common.c or somewhere in header. (arm has arch/arm/include/asm/traps.h for that purpose) Thanks, > > Thanks, > > Mathieu > > > > if (addr >= __irqentry_text_start && addr < __irqentry_text_end) > > return true; > > #endif > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com -- Masami Hiramatsu <mhira...@kernel.org>