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 <dave.hansen(a)linux.intel.com> Cc: Adam Buchbinder <adam.buchbinder(a)gmail.com> Cc: Colin Ian King <colin.king(a)canonical.com> Cc: Lorenzo Stoakes <lstoakes(a)gmail.com> Cc: Qiaowei Ren <qiaowei.ren(a)intel.com> Cc: Arnaldo Carvalho de Melo <acme(a)redhat.com> Cc: Masami Hiramatsu <mhiramat(a)kernel.org> Cc: Adrian Hunter <adrian.hunter(a)intel.com> Cc: Kees Cook <keescook(a)chromium.org> Cc: Thomas Garnier <thgarnie(a)google.com> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Borislav Petkov <bp(a)suse.de> Cc: Dmitry Vyukov <dvyukov(a)google.com> Cc: Ravi V. Shankar <ravi.v.shankar(a)intel.com> Cc: x86(a)kernel.org Signed-off-by: Ricardo Neri <ricardo.neri-calderon(a)linux.intel.com> --- 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 <linux/err.h> #include <asm/ptrace.h>
+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(&defs, 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) --