Re: [PATCH v7 13/26] x86/insn-eval: Add function to get default params of code segment

2017-06-15 Thread Ricardo Neri
On Wed, 2017-06-07 at 14:59 +0200, Borislav Petkov wrote:
> On Fri, May 05, 2017 at 11:17:11AM -0700, Ricardo Neri wrote:
> > This function returns the default values of the address and operand sizes
> > as specified in the segment descriptor. This information is determined
> > from the D and L bits. Hence, it can be used for both IA-32e 64-bit and
> > 32-bit legacy modes. For virtual-8086 mode, the default address and
> > operand sizes are always 2 bytes.
> > 
> > The D bit is only meaningful for code segments. Thus, these functions
> > always use the code segment selector contained in regs.
> > 
> > Cc: Dave Hansen 
> > Cc: Adam Buchbinder 
> > Cc: Colin Ian King 
> > Cc: Lorenzo Stoakes 
> > Cc: Qiaowei Ren 
> > Cc: Arnaldo Carvalho de Melo 
> > Cc: Masami Hiramatsu 
> > Cc: Adrian Hunter 
> > Cc: Kees Cook 
> > Cc: Thomas Garnier 
> > Cc: Peter Zijlstra 
> > Cc: Borislav Petkov 
> > Cc: Dmitry Vyukov 
> > Cc: Ravi V. Shankar 
> > Cc: x...@kernel.org
> > Signed-off-by: Ricardo Neri 
> > ---
> >  arch/x86/include/asm/insn-eval.h |  6 
> >  arch/x86/lib/insn-eval.c | 65 
> > 
> >  2 files changed, 71 insertions(+)
> > 
> > diff --git a/arch/x86/include/asm/insn-eval.h 
> > b/arch/x86/include/asm/insn-eval.h
> > index 7f3c7fe..9ed1c88 100644
> > --- a/arch/x86/include/asm/insn-eval.h
> > +++ b/arch/x86/include/asm/insn-eval.h
> > @@ -11,9 +11,15 @@
> >  #include 
> >  #include 
> >  
> > +struct insn_code_seg_defaults {
> 
> A whole struct for a function which gets called only once?
> 
> Bah, that's a bit too much, if you ask me.
> 
> So you're returning two small unsigned integers - i.e., you can just as
> well return a single u8 and put address and operand sizes in there:
> 
>   ret = oper_sz | addr_sz << 4;
> 
> No need for special structs for that.

OK. This makes sense. Perhaps I can use a couple of #define's to set and
get the the address and operand sizes in a single u8. This would make
the code more readable.

> 
> > +   unsigned char address_bytes;
> > +   unsigned char operand_bytes;
> > +};
> > +
> >  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);
> >  unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn,
> > int regoff);
> > +struct insn_code_seg_defaults insn_get_code_seg_defaults(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 c77ed80..693e5a8 100644
> > --- a/arch/x86/lib/insn-eval.c
> > +++ b/arch/x86/lib/insn-eval.c
> > @@ -603,6 +603,71 @@ static unsigned long get_seg_limit(struct pt_regs 
> > *regs, struct insn *insn,
> >  }
> >  
> >  /**
> > + * insn_get_code_seg_defaults() - Obtain code segment default parameters
> > + * @regs:  Structure with register values as seen when entering kernel mode
> > + *
> > + * Obtain the default parameters of the code segment: address and operand 
> > sizes.
> > + * The code segment is obtained from the selector contained in the CS 
> > register
> > + * in regs. In protected mode, the default address is determined by 
> > inspecting
> > + * the L and D bits of the segment descriptor. In virtual-8086 mode, the 
> > default
> > + * is always two bytes for both address and operand sizes.
> > + *
> > + * Return: A populated insn_code_seg_defaults structure on success. The
> > + * structure contains only zeros on failure.
> 
> s/failure/error/

Will correct.
> 
> > + */
> > +struct insn_code_seg_defaults insn_get_code_seg_defaults(struct pt_regs 
> > *regs)
> > +{
> > +   struct desc_struct *desc;
> > +   struct insn_code_seg_defaults defs;
> > +   unsigned short sel;
> > +   /*
> > +* The most significant byte of AR_TYPE_MASK determines whether a
> > +* segment contains data or code.
> > +*/
> > +   unsigned int type_mask = AR_TYPE_MASK & (1 << 11);
> > +
> > +   memset(, 0, sizeof(defs));
> > +
> > +   if (v8086_mode(regs)) {
> > +   defs.address_bytes = 2;
> > +   defs.operand_bytes = 2;
> > +   return defs;
> > +   }
> > +
> > +   sel = (unsigned short)regs->cs;
> > +
> > +   desc = get_desc(sel);
> > +   if (!desc)
> > +   return defs;
> > +
> > +   /* if data segment, return */
> > +   if (!(desc->b & type_mask))
> > +   return defs;
> 
> So you can simplify that into:
> 
>   /* A code segment? */
>   if (!(desc->b & BIT(11)))
>   return defs;
> 
> and remove that type_mask thing.

Alternatively, I can do desc->type & BIT(3) to avoid 

Re: [PATCH v7 13/26] x86/insn-eval: Add function to get default params of code segment

2017-06-07 Thread Borislav Petkov
On Fri, May 05, 2017 at 11:17:11AM -0700, Ricardo Neri wrote:
> This function returns the default values of the address and operand sizes
> as specified in the segment descriptor. This information is determined
> from the D and L bits. Hence, it can be used for both IA-32e 64-bit and
> 32-bit legacy modes. For virtual-8086 mode, the default address and
> operand sizes are always 2 bytes.
> 
> The D bit is only meaningful for code segments. Thus, these functions
> always use the code segment selector contained in regs.
> 
> Cc: Dave Hansen 
> Cc: Adam Buchbinder 
> Cc: Colin Ian King 
> Cc: Lorenzo Stoakes 
> Cc: Qiaowei Ren 
> Cc: Arnaldo Carvalho de Melo 
> Cc: Masami Hiramatsu 
> Cc: Adrian Hunter 
> Cc: Kees Cook 
> Cc: Thomas Garnier 
> Cc: Peter Zijlstra 
> Cc: Borislav Petkov 
> Cc: Dmitry Vyukov 
> Cc: Ravi V. Shankar 
> Cc: x...@kernel.org
> Signed-off-by: Ricardo Neri 
> ---
>  arch/x86/include/asm/insn-eval.h |  6 
>  arch/x86/lib/insn-eval.c | 65 
> 
>  2 files changed, 71 insertions(+)
> 
> diff --git a/arch/x86/include/asm/insn-eval.h 
> b/arch/x86/include/asm/insn-eval.h
> index 7f3c7fe..9ed1c88 100644
> --- a/arch/x86/include/asm/insn-eval.h
> +++ b/arch/x86/include/asm/insn-eval.h
> @@ -11,9 +11,15 @@
>  #include 
>  #include 
>  
> +struct insn_code_seg_defaults {

A whole struct for a function which gets called only once?

Bah, that's a bit too much, if you ask me.

So you're returning two small unsigned integers - i.e., you can just as
well return a single u8 and put address and operand sizes in there:

ret = oper_sz | addr_sz << 4;

No need for special structs for that.

> + unsigned char address_bytes;
> + unsigned char operand_bytes;
> +};
> +
>  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);
>  unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn,
>   int regoff);
> +struct insn_code_seg_defaults insn_get_code_seg_defaults(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 c77ed80..693e5a8 100644
> --- a/arch/x86/lib/insn-eval.c
> +++ b/arch/x86/lib/insn-eval.c
> @@ -603,6 +603,71 @@ static unsigned long get_seg_limit(struct pt_regs *regs, 
> struct insn *insn,
>  }
>  
>  /**
> + * insn_get_code_seg_defaults() - Obtain code segment default parameters
> + * @regs:Structure with register values as seen when entering kernel mode
> + *
> + * Obtain the default parameters of the code segment: address and operand 
> sizes.
> + * The code segment is obtained from the selector contained in the CS 
> register
> + * in regs. In protected mode, the default address is determined by 
> inspecting
> + * the L and D bits of the segment descriptor. In virtual-8086 mode, the 
> default
> + * is always two bytes for both address and operand sizes.
> + *
> + * Return: A populated insn_code_seg_defaults structure on success. The
> + * structure contains only zeros on failure.

s/failure/error/

> + */
> +struct insn_code_seg_defaults insn_get_code_seg_defaults(struct pt_regs 
> *regs)
> +{
> + struct desc_struct *desc;
> + struct insn_code_seg_defaults defs;
> + unsigned short sel;
> + /*
> +  * The most significant byte of AR_TYPE_MASK determines whether a
> +  * segment contains data or code.
> +  */
> + unsigned int type_mask = AR_TYPE_MASK & (1 << 11);
> +
> + memset(, 0, sizeof(defs));
> +
> + if (v8086_mode(regs)) {
> + defs.address_bytes = 2;
> + defs.operand_bytes = 2;
> + return defs;
> + }
> +
> + sel = (unsigned short)regs->cs;
> +
> + desc = get_desc(sel);
> + if (!desc)
> + return defs;
> +
> + /* if data segment, return */
> + if (!(desc->b & type_mask))
> + return defs;

So you can simplify that into:

/* A code segment? */
if (!(desc->b & BIT(11)))
return defs;

and remove that type_mask thing.

-- 
Regards/Gruss,
Boris.

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