Re: [v6 PATCH 05/21] x86/insn-eval: Add utility functions to get register offsets

[Borislav Petkov]

On Tue, Mar 07, 2017 at 04:32:38PM -0800, Ricardo Neri wrote:
> The function insn_get_reg_offset takes as argument an enumeration that

Please end function names with parentheses.

And do you mean get_reg_offset(), per chance?

> indicates the type of offset that is returned: the R/M part of the ModRM
> byte, the index of the SIB byte or the base of the SIB byte.

Err, you mean, it returns the offset to the register the argument
specifies.

> Callers of
> this function would need the definition of such enumeration. This is not
> needed. Instead, helper functions can be defined for this purpose can be
> added.

"Instead, add helpers... "

> 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 mod part of the ModRM byte.
> 
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Adam Buchbinder <adam.buchbinder@xxxxxxxxx>
> Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> Cc: Qiaowei Ren <qiaowei.ren@xxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Thomas Garnier <thgarnie@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/insn-eval.h |  3 +++
>  arch/x86/lib/insn-eval.c         | 51 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 54 insertions(+)
> 
> diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
> index 5cab1b1..754211b 100644
> --- a/arch/x86/include/asm/insn-eval.h
> +++ b/arch/x86/include/asm/insn-eval.h
> @@ -12,5 +12,8 @@
>  #include <asm/ptrace.h>
>  
>  void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
> +int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs);
> +int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);
> +int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);

Forgotten to edit the copy-paste?

Which means, nothing really needs insn_get_reg_offset_sib_index() and
you can get rid of it?

>  #endif /* _ASM_X86_INSN_EVAL_H */
> diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
> index 23cf010..78df1c9 100644
> --- a/arch/x86/lib/insn-eval.c
> +++ b/arch/x86/lib/insn-eval.c
> @@ -98,6 +98,57 @@ 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
> + * @insn:	Instruction structure containing the ModRM byte
> + * @regs:	Set of registers indicated by the ModRM byte

That's simply struct pt_regs - not a set of registers indicated by
ModRM?!?

> + * Obtain 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.

Put that sentence under the "Return: " paragraph below so that it is
immediately obvious what the retvals are.

> + *
> + * Return: Register indicated by r/m, as an offset within struct pt_regs
> + */
> +int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs)

That name is too long: insn_get_modrm_rm_off() should be enough.

> +{
> +	return get_reg_offset(insn, regs, REG_TYPE_RM);
> +}
> +
> +/**
> + * insn_get_reg_offset_sib_base - Obtain register in base part of SiB byte
> + * @insn:	Instruction structure containing the SiB byte
> + * @regs:	Set of registers indicated by the SiB byte
> + *
> + * Obtain the register indicated by the base part of the SiB 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 SiB does not refer to a register.
> + *
> + * Return: Register indicated by SiB's base, as an offset within struct pt_regs

Let's stick to a single spelling: SIB, all caps.

> + */
> +int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs)

insn_get_sib_base_off()

Ditto for the rest of the comments on insn_get_reg_offset_modrm_rm() above.

> +{
> +	return get_reg_offset(insn, regs, REG_TYPE_BASE);
> +}
> +
> +/**
> + * insn_get_reg_offset_sib_index - Obtain register in index part of SiB byte
> + * @insn:	Instruction structure containing the SiB byte
> + * @regs:	Set of registers indicated by the SiB byte
> + *
> + * Obtain the register indicated by the index part of the SiB byte. The
> + * register is obtained as an offset from the index of pt_regs. In specific
> + * cases, the returned value can be -EDOM to indicate that the particular value
> + * of SiB does not refer to a register.
> + *
> + * Return: Register indicated by SiB's base, as an offset within struct pt_regs
> + */
> +int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)

insn_get_sib_idx_off()

And again, if this function is unused, don't add it.

Thanks.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix ImendÃrffer, Jane Smithard, Graham Norton, HRB 21284 (AG NÃrnberg)
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