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Re: [PATCH v7 08/26] x86/insn-eval: Add a utility function to get register offsets

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  Re: [PATCH v7 08/26] x86/insn-eval: Add a utility function to get  register offsets Borislav Petkov <bp@suse.de> - 2017-05-29 19:20 +0200
    Re: [PATCH v7 08/26] x86/insn-eval: Add a utility function to get  register offsets Ricardo Neri <ricardo.neri-calderon@linux.intel.com> - 2017-06-06 08:10 +0200

#1652669 — Re: [PATCH v7 08/26] x86/insn-eval: Add a utility function to get register offsets

On Fri, May 05, 2017 at 11:17:06AM -0700, Ricardo Neri wrote:
> The function get_reg_offset() returns the offset to the register the
> argument specifies as indicated in an enumeration of type offset. Callers
> of this function would need the definition of such enumeration. This is
> not needed. Instead, add helper functions for this purpose. These functions
> are useful in cases when, for instance, the caller needs to decide whether
> the operand is a register or a memory location by looking at the rm part
> of the ModRM byte. As of now, this is the only helper function that is
> needed.
> 
> 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-eval.h |  1 +
>  arch/x86/lib/insn-eval.c         | 15 +++++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
> index 5cab1b1..7e8c963 100644
> --- a/arch/x86/include/asm/insn-eval.h
> +++ b/arch/x86/include/asm/insn-eval.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_modrm_rm_off(struct insn *insn, struct pt_regs *regs);
>  
>  #endif /* _ASM_X86_INSN_EVAL_H */
> diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
> index 182e2ae..8b16761 100644
> --- a/arch/x86/lib/insn-eval.c
> +++ b/arch/x86/lib/insn-eval.c
> @@ -97,6 +97,21 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
>  	return regoff[regno];
>  }
>  
> +/**
> + * insn_get_reg_offset_modrm_rm() - Obtain register in r/m part of ModRM byte

That name needs to be synced with the function name below.

> + * @insn:	Instruction structure containing the ModRM byte
> + * @regs:	Structure with register values as seen when entering kernel mode
> + *
> + * Return: The register indicated by the r/m part of the ModRM byte. The
> + * register is obtained as an offset from the base of pt_regs. In specific
> + * cases, the returned value can be -EDOM to indicate that the particular value
> + * of ModRM does not refer to a register and shall be ignored.
> + */
> +int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs)
	^^^^^^^^^^^^^^^^^^^^

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

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#1658373

On Mon, 2017-05-29 at 19:16 +0200, Borislav Petkov wrote:
> On Fri, May 05, 2017 at 11:17:06AM -0700, Ricardo Neri wrote:
> > The function get_reg_offset() returns the offset to the register the
> > argument specifies as indicated in an enumeration of type offset. Callers
> > of this function would need the definition of such enumeration. This is
> > not needed. Instead, add helper functions for this purpose. These functions
> > are useful in cases when, for instance, the caller needs to decide whether
> > the operand is a register or a memory location by looking at the rm part
> > of the ModRM byte. As of now, this is the only helper function that is
> > needed.
> > 
> > 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-eval.h |  1 +
> >  arch/x86/lib/insn-eval.c         | 15 +++++++++++++++
> >  2 files changed, 16 insertions(+)
> > 
> > diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
> > index 5cab1b1..7e8c963 100644
> > --- a/arch/x86/include/asm/insn-eval.h
> > +++ b/arch/x86/include/asm/insn-eval.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_modrm_rm_off(struct insn *insn, struct pt_regs *regs);
> >  
> >  #endif /* _ASM_X86_INSN_EVAL_H */
> > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
> > index 182e2ae..8b16761 100644
> > --- a/arch/x86/lib/insn-eval.c
> > +++ b/arch/x86/lib/insn-eval.c
> > @@ -97,6 +97,21 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
> >  	return regoff[regno];
> >  }
> >  
> > +/**
> > + * insn_get_reg_offset_modrm_rm() - Obtain register in r/m part of ModRM byte
> 
> That name needs to be synced with the function name below.

Ugh! I missed this. I will update accordingly. Thanks for the detailed
review.

BR,
Ricardo

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