Messages in this thread | | | Date | Fri, 14 Aug 2020 15:36:06 -0700 (PDT) | Subject | Re: [PATCH v3 3/7] riscv: Fixup kprobes handler couldn't change pc | From | Palmer Dabbelt <> |
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On Mon, 13 Jul 2020 16:39:18 PDT (-0700), guoren@kernel.org wrote: > From: Guo Ren <guoren@linux.alibaba.com> > > The "Changing Execution Path" section in the Documentation/kprobes.txt > said: > > Since kprobes can probe into a running kernel code, it can change the > register set, including instruction pointer. > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com> > Cc: Masami Hiramatsu <mhiramat@kernel.org> > Cc: Palmer Dabbelt <palmerdabbelt@google.com> > --- > arch/riscv/kernel/mcount-dyn.S | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S > index 35a6ed7..4b58b54 100644 > --- a/arch/riscv/kernel/mcount-dyn.S > +++ b/arch/riscv/kernel/mcount-dyn.S > @@ -123,6 +123,7 @@ ENDPROC(ftrace_caller) > sd ra, (PT_SIZE_ON_STACK+8)(sp) > addi s0, sp, (PT_SIZE_ON_STACK+16) > > + sd ra, PT_EPC(sp) > sd x1, PT_RA(sp) > sd x2, PT_SP(sp) > sd x3, PT_GP(sp)
So that's definately not going to be EPC any more. I'm not sure that field is sanely named, though, as it's really just the PC when it comes to other ptrace stuff.
> @@ -157,6 +158,7 @@ ENDPROC(ftrace_caller) > .endm > > .macro RESTORE_ALL > + ld ra, PT_EPC(sp) > ld x1, PT_RA(sp)
x1 is ra, so loading it twice doesn't seem reasonable.
> ld x2, PT_SP(sp) > ld x3, PT_GP(sp) > @@ -190,7 +192,6 @@ ENDPROC(ftrace_caller) > ld x31, PT_T6(sp) > > ld s0, (PT_SIZE_ON_STACK)(sp) > - ld ra, (PT_SIZE_ON_STACK+8)(sp) > addi sp, sp, (PT_SIZE_ON_STACK+16) > .endm
If you're dropping the load you should drop the store above as well. In general this seems kind of mixed up, both before and after this patch.
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