On Thu, 2017-04-20 at 15:06 +0200, Borislav Petkov wrote:
On Tue, Mar 07, 2017 at 04:32:42PM -0800, Ricardo Neri wrote:
These functions read 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.
Yeah, we tend to call that customarily 16-bit :)
I will call it like this.
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@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 | 2 + arch/x86/lib/insn-eval.c | 80 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 82 insertions(+)
diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h index b201742..a0d81fc 100644 --- a/arch/x86/include/asm/insn-eval.h +++ b/arch/x86/include/asm/insn-eval.h @@ -15,6 +15,8 @@ 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); +unsigned char insn_get_seg_default_address_bytes(struct pt_regs *regs); +unsigned char insn_get_seg_default_operand_bytes(struct pt_regs *regs); unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn, int regoff, bool use_default_seg);
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 383ca83..cda6c71 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -421,6 +421,86 @@ unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn, }
/**
- insn_get_seg_default_address_bytes - Obtain default address size of segment
- @regs: Set of registers containing the segment selector
- Obtain the default address size as indicated in the segment descriptor
- selected in regs' code segment selector. 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.
- Return: Default address size of segment
0 on error.
- */
+unsigned char insn_get_seg_default_address_bytes(struct pt_regs *regs) +{
- struct desc_struct *desc;
- unsigned short seg;
- int ret;
- if (v8086_mode(regs))
return 2;- seg = (unsigned short)regs->cs;
- ret = get_desc(seg, &desc);
- if (ret)
return 0;- switch ((desc->l << 1) | desc->d) {
- case 0: /* Legacy mode. 16-bit addresses. CS.L=0, CS.D=0 */
return 2;- case 1: /* Legacy mode. 32-bit addresses. CS.L=0, CS.D=1 */
return 4;- case 2: /* IA-32e 64-bit mode. 64-bit addresses. CS.L=1, CS.D=0 */
return 8;- case 3: /* Invalid setting. CS.L=1, CS.D=1 */
/* fall through */- default:
return 0;- }
+}
+/**
- insn_get_seg_default_operand_bytes - Obtain default operand size of segment
- @regs: Set of registers containing the segment selector
- Obtain the default operand size as indicated in the segment descriptor
- selected in regs' code segment selector. In protected mode, the default
- operand size is determined by inspecting the L and D bits of the segment
- descriptor. In virtual-8086 mode, the default is always two bytes.
- Return: Default operand size of segment
- */
+unsigned char insn_get_seg_default_operand_bytes(struct pt_regs *regs)
Right, so default address and operand size always go together so I don't think you need two separate functions.
So what I'd suggest - provided this pans out (I still haven't reviewed the whole thing) - is to determine the operating mode of the segment: long, legacy, etc and then return both address and operand sizes. Patch 17/21 needs them both at the same time AFAICT.
It makes sense to me. So far these two functions are used in the same place.
Thanks and BR, Ricardo