x86/insn-eval: Add function to get default params of code segment
Obtain the default values of the address and operand sizes as specified in the D and L bits of the the segment descriptor selected by the register CS. The function can be used for both protected and long modes. For virtual-8086 mode, the default address and operand sizes are always 2 bytes. The returned parameters are encoded in a signed 8-bit data type. Auxiliar macros are provided to encode and decode such values. Improvements-by: Borislav Petkov <bp@suse.de> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Borislav Petkov <bp@suse.de> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: ricardo.neri@intel.com Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Huang Rui <ray.huang@amd.com> Cc: Qiaowei Ren <qiaowei.ren@intel.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com> Cc: Chris Metcalf <cmetcalf@mellanox.com> Cc: Brian Gerst <brgerst@gmail.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Colin Ian King <colin.king@canonical.com> Cc: Chen Yucong <slaoub@gmail.com> Cc: Adam Buchbinder <adam.buchbinder@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Thomas Garnier <thgarnie@google.com> Link: https://lkml.kernel.org/r/1509135945-13762-17-git-send-email-ricardo.neri-calderon@linux.intel.com
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@ -11,8 +11,13 @@
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#include <linux/err.h>
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#include <asm/ptrace.h>
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#define INSN_CODE_SEG_ADDR_SZ(params) ((params >> 4) & 0xf)
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#define INSN_CODE_SEG_OPND_SZ(params) (params & 0xf)
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#define INSN_CODE_SEG_PARAMS(oper_sz, addr_sz) (oper_sz | (addr_sz << 4))
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void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
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int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs);
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unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx);
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char insn_get_code_seg_params(struct pt_regs *regs);
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#endif /* _ASM_X86_INSN_EVAL_H */
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@ -639,6 +639,70 @@ static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx)
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return limit;
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}
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/**
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* insn_get_code_seg_params() - Obtain code segment parameters
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* @regs: Structure with register values as seen when entering kernel mode
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*
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* Obtain address and operand sizes of the code segment. It is obtained from the
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* selector contained in the CS register in regs. In protected mode, the default
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* address is determined by inspecting the L and D bits of the segment
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* descriptor. In virtual-8086 mode, the default is always two bytes for both
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* address and operand sizes.
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*
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* Returns:
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*
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* A signed 8-bit value containing the default parameters on success.
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*
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* -EINVAL on error.
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*/
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char insn_get_code_seg_params(struct pt_regs *regs)
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{
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struct desc_struct *desc;
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short sel;
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if (v8086_mode(regs))
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/* Address and operand size are both 16-bit. */
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return INSN_CODE_SEG_PARAMS(2, 2);
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sel = get_segment_selector(regs, INAT_SEG_REG_CS);
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if (sel < 0)
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return sel;
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desc = get_desc(sel);
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if (!desc)
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return -EINVAL;
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/*
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* The most significant byte of the Type field of the segment descriptor
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* determines whether a segment contains data or code. If this is a data
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* segment, return error.
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*/
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if (!(desc->type & BIT(3)))
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return -EINVAL;
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switch ((desc->l << 1) | desc->d) {
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case 0: /*
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* Legacy mode. CS.L=0, CS.D=0. Address and operand size are
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* both 16-bit.
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*/
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return INSN_CODE_SEG_PARAMS(2, 2);
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case 1: /*
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* Legacy mode. CS.L=0, CS.D=1. Address and operand size are
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* both 32-bit.
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*/
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return INSN_CODE_SEG_PARAMS(4, 4);
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case 2: /*
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* IA-32e 64-bit mode. CS.L=1, CS.D=0. Address size is 64-bit;
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* operand size is 32-bit.
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*/
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return INSN_CODE_SEG_PARAMS(4, 8);
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case 3: /* Invalid setting. CS.L=1, CS.D=1 */
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/* fall through */
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default:
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return -EINVAL;
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}
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}
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/**
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* insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte
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* @insn: Instruction containing the ModRM byte
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