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

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