The insn-eval.c library was recently imported from the kernel source and contains a significant amount of code to support legacy x86 operating modes, such as 32-bit protected mode, 16-bit addressing, and v8086 mode.
The KVM selftests, particularly for features like SEV-ES, exclusively target the 64-bit architecture with guest kernel running in kernel mode. Simplify the decoder by removing all logic not relevant to 64-bit mode. This involves: - Remove all CONFIG_X86_32 and v8086_mode conditional logic. - Simplify resolve_default_seg to always assume 64-bit segmentation rules (i.e., most segments are ignored). - Rework insn_get_seg_base to only handle the 64-bit model where FS/GS bases are read from MSRs. - Delete support for 16-bit address decoding. - Remove complex segment descriptor lookups, which are not used in the 64-bit flat memory model. This makes the library smaller and easier to maintain for its intended purpose within the selftests. Signed-off-by: Neeraj Upadhyay <[email protected]> --- .../testing/selftests/kvm/lib/x86/insn-eval.c | 254 ++---------------- 1 file changed, 28 insertions(+), 226 deletions(-) diff --git a/tools/testing/selftests/kvm/lib/x86/insn-eval.c b/tools/testing/selftests/kvm/lib/x86/insn-eval.c index a47c01977e72..cf751e4e36ec 100644 --- a/tools/testing/selftests/kvm/lib/x86/insn-eval.c +++ b/tools/testing/selftests/kvm/lib/x86/insn-eval.c @@ -178,52 +178,7 @@ static bool check_seg_overrides(struct insn *insn, int regoff) */ static int resolve_default_seg(struct insn *insn, struct pt_regs *regs, int off) { - if (any_64bit_mode(regs)) - return INAT_SEG_REG_IGNORE; - /* - * Resolve the default segment register as described in Section 3.7.4 - * of the Intel Software Development Manual Vol. 1: - * - * + DS for all references involving r[ABCD]X, and rSI. - * + If used in a string instruction, ES for rDI. Otherwise, DS. - * + AX, CX and DX are not valid register operands in 16-bit address - * encodings but are valid for 32-bit and 64-bit encodings. - * + -EDOM is reserved to identify for cases in which no register - * is used (i.e., displacement-only addressing). Use DS. - * + SS for rSP or rBP. - * + CS for rIP. - */ - - switch (off) { - case offsetof(struct pt_regs, ax): - case offsetof(struct pt_regs, cx): - case offsetof(struct pt_regs, dx): - /* Need insn to verify address size. */ - if (insn->addr_bytes == 2) - return -EINVAL; - - fallthrough; - - case -EDOM: - case offsetof(struct pt_regs, bx): - case offsetof(struct pt_regs, si): - return INAT_SEG_REG_DS; - - case offsetof(struct pt_regs, di): - if (is_string_insn(insn)) - return INAT_SEG_REG_ES; - return INAT_SEG_REG_DS; - - case offsetof(struct pt_regs, bp): - case offsetof(struct pt_regs, sp): - return INAT_SEG_REG_SS; - - case offsetof(struct pt_regs, ip): - return INAT_SEG_REG_CS; - - default: - return -EINVAL; - } + return INAT_SEG_REG_IGNORE; } /** @@ -288,12 +243,8 @@ static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff) * be used. Hence, it is not necessary to inspect the instruction, * which may be invalid at this point. */ - if (regoff == offsetof(struct pt_regs, ip)) { - if (any_64bit_mode(regs)) - return INAT_SEG_REG_IGNORE; - else - return INAT_SEG_REG_CS; - } + if (regoff == offsetof(struct pt_regs, ip)) + return INAT_SEG_REG_IGNORE; if (!insn) return -EINVAL; @@ -312,11 +263,8 @@ static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff) * In long mode, segment override prefixes are ignored, except for * overrides for FS and GS. */ - if (any_64bit_mode(regs)) { - if (idx != INAT_SEG_REG_FS && - idx != INAT_SEG_REG_GS) - idx = INAT_SEG_REG_IGNORE; - } + if (idx != INAT_SEG_REG_FS && idx != INAT_SEG_REG_GS) + idx = INAT_SEG_REG_IGNORE; return idx; } @@ -327,11 +275,9 @@ static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff) * @seg_reg_idx: Segment register index to use * * Obtain the segment selector from any of the CS, SS, DS, ES, FS, GS segment - * registers. In CONFIG_X86_32, the segment is obtained from either pt_regs or - * kernel_vm86_regs as applicable. In CONFIG_X86_64, CS and SS are obtained - * from pt_regs. DS, ES, FS and GS are obtained by reading the actual CPU - * registers. This done for only for completeness as in CONFIG_X86_64 segment - * registers are ignored. + * registers. CS and SS are obtained from pt_regs. DS, ES, FS and GS are + * obtained by reading the actual CPU registers. This done for only for + * completeness as in X86_64 segment registers are ignored. * * Returns: * @@ -344,7 +290,6 @@ static short get_segment_selector(struct pt_regs *regs, int seg_reg_idx) { unsigned short sel; -#ifdef CONFIG_X86_64 switch (seg_reg_idx) { case INAT_SEG_REG_IGNORE: return 0; @@ -367,48 +312,6 @@ static short get_segment_selector(struct pt_regs *regs, int seg_reg_idx) default: return -EINVAL; } -#else /* CONFIG_X86_32 */ - struct kernel_vm86_regs *vm86regs = (struct kernel_vm86_regs *)regs; - - if (v8086_mode(regs)) { - switch (seg_reg_idx) { - case INAT_SEG_REG_CS: - return (unsigned short)(regs->cs & 0xffff); - case INAT_SEG_REG_SS: - return (unsigned short)(regs->ss & 0xffff); - case INAT_SEG_REG_DS: - return vm86regs->ds; - case INAT_SEG_REG_ES: - return vm86regs->es; - case INAT_SEG_REG_FS: - return vm86regs->fs; - case INAT_SEG_REG_GS: - return vm86regs->gs; - case INAT_SEG_REG_IGNORE: - default: - return -EINVAL; - } - } - - switch (seg_reg_idx) { - case INAT_SEG_REG_CS: - return (unsigned short)(regs->cs & 0xffff); - case INAT_SEG_REG_SS: - return (unsigned short)(regs->ss & 0xffff); - case INAT_SEG_REG_DS: - return (unsigned short)(regs->ds & 0xffff); - case INAT_SEG_REG_ES: - return (unsigned short)(regs->es & 0xffff); - case INAT_SEG_REG_FS: - return (unsigned short)(regs->fs & 0xffff); - case INAT_SEG_REG_GS: - savesegment(gs, sel); - return sel; - case INAT_SEG_REG_IGNORE: - default: - return -EINVAL; - } -#endif /* CONFIG_X86_64 */ } static const int pt_regoff[] = { @@ -420,7 +323,6 @@ static const int pt_regoff[] = { offsetof(struct pt_regs, bp), offsetof(struct pt_regs, si), offsetof(struct pt_regs, di), -#ifdef CONFIG_X86_64 offsetof(struct pt_regs, r8), offsetof(struct pt_regs, r9), offsetof(struct pt_regs, r10), @@ -429,12 +331,6 @@ static const int pt_regoff[] = { offsetof(struct pt_regs, r13), offsetof(struct pt_regs, r14), offsetof(struct pt_regs, r15), -#else - offsetof(struct pt_regs, ds), - offsetof(struct pt_regs, es), - offsetof(struct pt_regs, fs), - offsetof(struct pt_regs, gs), -#endif }; int pt_regs_offset(struct pt_regs *regs, int regno) @@ -453,9 +349,6 @@ static int get_regno(struct insn *insn, enum reg_type type) * Don't possibly decode a 32-bit instructions as * reading a 64-bit-only register. */ - if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64) - nr_registers -= 8; - switch (type) { case REG_TYPE_RM: regno = X86_MODRM_RM(insn->modrm.value); @@ -687,52 +580,33 @@ static bool get_desc(struct desc_struct *out, unsigned short sel) */ unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx) { - struct desc_struct desc; + unsigned long base; short sel; sel = get_segment_selector(regs, seg_reg_idx); if (sel < 0) return -1L; - if (v8086_mode(regs)) - /* - * Base is simply the segment selector shifted 4 - * bits to the right. - */ - return (unsigned long)(sel << 4); + /* + * Only FS or GS will have a base address, the rest of + * the segments' bases are forced to 0. + */ - if (any_64bit_mode(regs)) { + if (seg_reg_idx == INAT_SEG_REG_FS) { + rdmsrq(MSR_FS_BASE, base); + } else if (seg_reg_idx == INAT_SEG_REG_GS) { /* - * Only FS or GS will have a base address, the rest of - * the segments' bases are forced to 0. + * swapgs was called at the kernel entry point. Thus, + * MSR_KERNEL_GS_BASE will have the user-space GS base. */ - unsigned long base; - - if (seg_reg_idx == INAT_SEG_REG_FS) { - rdmsrq(MSR_FS_BASE, base); - } else if (seg_reg_idx == INAT_SEG_REG_GS) { - /* - * swapgs was called at the kernel entry point. Thus, - * MSR_KERNEL_GS_BASE will have the user-space GS base. - */ - if (user_mode(regs)) - rdmsrq(MSR_KERNEL_GS_BASE, base); - else - rdmsrq(MSR_GS_BASE, base); - } else { - base = 0; - } - return base; + if (user_mode(regs)) + rdmsrq(MSR_KERNEL_GS_BASE, base); + else + rdmsrq(MSR_GS_BASE, base); + } else { + base = 0; } - - /* In protected mode the segment selector cannot be null. */ - if (!sel) - return -1L; - - if (!get_desc(&desc, sel)) - return -1L; - - return get_desc_base(&desc); + return base; } /** @@ -762,26 +636,7 @@ static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx) if (sel < 0) return 0; - if (any_64bit_mode(regs) || v8086_mode(regs)) - return -1L; - - if (!sel) - return 0; - - if (!get_desc(&desc, sel)) - return 0; - - /* - * If the granularity bit is set, the limit is given in multiples - * of 4096. This also means that the 12 least significant bits are - * not tested when checking the segment limits. In practice, - * this means that the segment ends in (limit << 12) + 0xfff. - */ - limit = get_desc_limit(&desc); - if (desc.g) - limit = (limit << 12) + 0xfff; - - return limit; + return -1L; } /** @@ -805,10 +660,6 @@ int insn_get_code_seg_params(struct pt_regs *regs) struct desc_struct desc; short sel; - if (v8086_mode(regs)) - /* Address and operand size are both 16-bit. */ - return INSN_CODE_SEG_PARAMS(2, 2); - sel = get_segment_selector(regs, INAT_SEG_REG_CS); if (sel < 0) return sel; @@ -1042,10 +893,7 @@ static int get_eff_addr_modrm(struct insn *insn, struct pt_regs *regs, * following instruction. */ if (*regoff == -EDOM) { - if (any_64bit_mode(regs)) - tmp = regs->ip + insn->length; - else - tmp = 0; + tmp = regs->ip + insn->length; } else if (*regoff < 0) { return -EINVAL; } else { @@ -1277,9 +1125,6 @@ static void __user *get_addr_ref_16(struct insn *insn, struct pt_regs *regs) linear_addr = (unsigned long)(eff_addr & 0xffff) + seg_base; - /* Limit linear address to 20 bits */ - if (v8086_mode(regs)) - linear_addr &= 0xfffff; out: return (void __user *)linear_addr; @@ -1338,27 +1183,6 @@ static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs) if (ret) goto out; - /* - * In protected mode, before computing the linear address, make sure - * the effective address is within the limits of the segment. - * 32-bit addresses can be used in long and virtual-8086 modes if an - * address override prefix is used. In such cases, segment limits are - * not enforced. When in virtual-8086 mode, the segment limit is -1L - * to reflect this situation. - * - * After computed, the effective address is treated as an unsigned - * quantity. - */ - if (!any_64bit_mode(regs) && ((unsigned int)eff_addr > seg_limit)) - goto out; - - /* - * Even though 32-bit address encodings are allowed in virtual-8086 - * mode, the address range is still limited to [0x-0xffff]. - */ - if (v8086_mode(regs) && (eff_addr & ~0xffff)) - goto out; - /* * Data type long could be 64 bits in size. Ensure that our 32-bit * effective address is not sign-extended when computing the linear @@ -1366,9 +1190,6 @@ static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs) */ linear_addr = (unsigned long)(eff_addr & 0xffffffff) + seg_base; - /* Limit linear address to 20 bits */ - if (v8086_mode(regs)) - linear_addr &= 0xfffff; out: return (void __user *)linear_addr; @@ -1389,12 +1210,6 @@ static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs) * * -1L on error. */ -#ifndef CONFIG_X86_64 -static void __user *get_addr_ref_64(struct insn *insn, struct pt_regs *regs) -{ - return (void __user *)-1L; -} -#else static void __user *get_addr_ref_64(struct insn *insn, struct pt_regs *regs) { unsigned long linear_addr = -1L, seg_base; @@ -1431,7 +1246,6 @@ static void __user *get_addr_ref_64(struct insn *insn, struct pt_regs *regs) out: return (void __user *)linear_addr; } -#endif /* CONFIG_X86_64 */ /** * insn_get_addr_ref() - Obtain the linear address referred by instruction @@ -1472,18 +1286,6 @@ int insn_get_effective_ip(struct pt_regs *regs, unsigned long *ip) { unsigned long seg_base = 0; - /* - * If not in user-space long mode, a custom code segment could be in - * use. This is true in protected mode (if the process defined a local - * descriptor table), or virtual-8086 mode. In most of the cases - * seg_base will be zero as in USER_CS. - */ - if (!user_64bit_mode(regs)) { - seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS); - if (seg_base == -1L) - return -EINVAL; - } - *ip = seg_base + regs->ip; return 0; @@ -1563,7 +1365,7 @@ bool insn_decode_from_regs(struct insn *insn, struct pt_regs *regs, { int seg_defs; - insn_init(insn, buf, buf_size, user_64bit_mode(regs)); + insn_init(insn, buf, buf_size, true); /* * Override the default operand and address sizes with what is specified -- 2.34.1
