Re: [PATCH v7 13/26] x86/insn-eval: Add function to get default params of code segment
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
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) -- -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html