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.
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 + */ +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) +{ + 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 or 8-bit operands CS.L=0, CS.D=0 */ + return 2; + case 1: /* Legacy mode. 32- or 8 bit operands CS.L=0, CS.D=1 */ + /* fall through */ + case 2: /* IA-32e 64-bit mode. 32- or 8-bit opnds. CS.L=1, CS.D=0 */ + return 4; + case 3: /* Invalid setting. CS.L=1, CS.D=1 */ + /* fall through */ + default: + return 0; + } +} + +/** * 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