Re: [v3 PATCH 04/10] x86/insn-kernel: Add a function to obtain register offset in ModRM

Masami Hiramatsu
2017-01-27T07:53:31Z

On Wed, 25 Jan 2017 22:07:16 -0800
Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote:

> Hi Masami,
>
> On Thu, 2017-01-26 at 11:11 +0900, Masami Hiramatsu wrote:
> > On Wed, 25 Jan 2017 12:23:47 -0800
> > Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote:
> >
> > > The function insn_get_reg_offset requires a type to indicate whether
> > > the returned offset is that given by by the ModRM or the SIB byte.
> > > Callers of this function would need the definition of the type struct.
> > > This is not needed. Instead, auxiliary functions can be defined for
> > > this purpose.
> > >
> > > When the operand is a register, the emulation code for User-Mode
> > > Instruction Prevention needs to know the offset of the register indicated
> > > in the r/m part of the ModRM byte. Thus, start by adding an auxiliary
> > > function for this purpose.
> >
> > Hmm, why wouldn't you just rename it to insn_get_reg_offset() and export it?
>
> Do you mean exporting the structure that I mention above? The problem
> that I am trying to solve is that callers sometimes want to know the
> offset of the register encoded in the SiB or the ModRM bytes. I could
> use something
>
> insn_get_reg_offset(insn, regs, INSN_TYPE_MODRM)
> insn_get_reg_offset(insn, regs, INSN_TYPE_SIB)
>
> Instead, I opted for
>
> insn_get_reg_offset_rm(insn, regs)
> insn_get_reg_offset_sib(insn, regs)
>
> to avoid exposing an enum with the INSN_TYPE_MODRM, INSN_TYPE_SIB.

OK, if so, I think you should export both of them at once, not only
insn_get_reg_offset_rm().

Thank you,

>
> If you feel that the former makes more sense, I can change the
> implementation.
>
> Thanks and BR,
> Ricardo
> >
> > Thank you,
> >
> > >
> > > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > > Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
> > > Cc: Colin Ian King <colin.king@canonical.com>
> > > Cc: Lorenzo Stoakes <lstoakes@gmail.com>
> > > Cc: Qiaowei Ren <qiaowei.ren@intel.com>
> > > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > > Cc: Masami Hiramatsu <mhiramat@kernel.org>
> > > Cc: Adrian Hunter <adrian.hunter@intel.com>
> > > Cc: Kees Cook <keescook@chromium.org>
> > > Cc: Thomas Garnier <thgarnie@google.com>
> > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > Cc: Borislav Petkov <bp@suse.de>
> > > Cc: Dmitry Vyukov <dvyukov@google.com>
> > > Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
> > > Cc: x86@kernel.org
> > > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> > > ---
> > > arch/x86/include/asm/insn-kernel.h | 1 +
> > > arch/x86/lib/insn-kernel.c | 5 +++++
> > > 2 files changed, 6 insertions(+)
> > >
> > > diff --git a/arch/x86/include/asm/insn-kernel.h b/arch/x86/include/asm/insn-kernel.h
> > > index aef416a..3f34649 100644
> > > --- a/arch/x86/include/asm/insn-kernel.h
> > > +++ b/arch/x86/include/asm/insn-kernel.h
> > > @@ -12,5 +12,6 @@
> > > #include <asm/ptrace.h>
> > >
> > > void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
> > > +int insn_get_reg_offset_rm(struct insn *insn, struct pt_regs *regs);
> > >
> > > #endif /* _ASM_X86_INSN_KERNEL_H */
> > > diff --git a/arch/x86/lib/insn-kernel.c b/arch/x86/lib/insn-kernel.c
> > > index 8072abe..267cab4 100644
> > > --- a/arch/x86/lib/insn-kernel.c
> > > +++ b/arch/x86/lib/insn-kernel.c
> > > @@ -95,6 +95,11 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
> > > return regoff[regno];
> > > }
> > >
> > > +int insn_get_reg_offset_rm(struct insn *insn, struct pt_regs *regs)
> > > +{
> > > + return get_reg_offset(insn, regs, REG_TYPE_RM);
> > > +}
> > > +
> > > /*
> > > * return the address being referenced be instruction
> > > * for rm=3 returning the content of the rm reg
> > > --
> > > 2.9.3
> > >
> >
> >
>
>

--
Masami Hiramatsu <mhiramat@kernel.org>