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authorRicardo Neri <ricardo.neri-calderon@linux.intel.com>2017-11-06 05:27:50 +0300
committerIngo Molnar <mingo@kernel.org>2017-11-08 13:16:20 +0300
commit9c6c799faeed54b17857c2eed9058a25b8ee3614 (patch)
treea3c20930480e57d917f904d8fade8bbfc6d34e4f /arch/x86/lib
parent86cc35109029b7f1b195cef6c74654bad95e81af (diff)
downloadlinux-9c6c799faeed54b17857c2eed9058a25b8ee3614.tar.xz
x86/insn-eval: Add support to resolve 16-bit address encodings
Tasks running in virtual-8086 mode, in protected mode with code segment descriptors that specify 16-bit default address sizes via the D bit, or via an address override prefix will use 16-bit addressing form encodings as described in the Intel 64 and IA-32 Architecture Software Developer's Manual Volume 2A Section 2.1.5, Table 2-1. 16-bit addressing encodings differ in several ways from the 32-bit/64-bit addressing form encodings: ModRM.rm points to different registers and, in some cases, effective addresses are indicated by the addition of the value of two registers. Also, there is no support for SIB bytes. Thus, a separate function is needed to parse this form of addressing. Three functions are introduced. get_reg_offset_16() obtains the offset from the base of pt_regs of the registers indicated by the ModRM byte of the address encoding. get_eff_addr_modrm_16() computes the effective address from the value of the register operands. get_addr_ref_16() computes the linear address using the obtained effective address and the base address of the segment. Segment limits are enforced when running in protected mode. Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Adam Buchbinder <adam.buchbinder@gmail.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Borislav Petkov <bp@suse.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Chen Yucong <slaoub@gmail.com> Cc: Chris Metcalf <cmetcalf@mellanox.com> Cc: Colin Ian King <colin.king@canonical.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Huang Rui <ray.huang@amd.com> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Qiaowei Ren <qiaowei.ren@intel.com> Cc: Ravi V. Shankar <ravi.v.shankar@intel.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Garnier <thgarnie@google.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: ricardo.neri@intel.com Link: http://lkml.kernel.org/r/1509935277-22138-6-git-send-email-ricardo.neri-calderon@linux.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/lib')
-rw-r--r--arch/x86/lib/insn-eval.c213
1 files changed, 212 insertions, 1 deletions
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index ef102db43289..35625d279458 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -481,6 +481,80 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
}
/**
+ * get_reg_offset_16() - Obtain offset of register indicated by instruction
+ * @insn: Instruction containing ModRM byte
+ * @regs: Register values as seen when entering kernel mode
+ * @offs1: Offset of the first operand register
+ * @offs2: Offset of the second opeand register, if applicable
+ *
+ * Obtain the offset, in pt_regs, of the registers indicated by the ModRM byte
+ * in @insn. This function is to be used with 16-bit address encodings. The
+ * @offs1 and @offs2 will be written with the offset of the two registers
+ * indicated by the instruction. In cases where any of the registers is not
+ * referenced by the instruction, the value will be set to -EDOM.
+ *
+ * Returns:
+ *
+ * 0 on success, -EINVAL on error.
+ */
+static int get_reg_offset_16(struct insn *insn, struct pt_regs *regs,
+ int *offs1, int *offs2)
+{
+ /*
+ * 16-bit addressing can use one or two registers. Specifics of
+ * encodings are given in Table 2-1. "16-Bit Addressing Forms with the
+ * ModR/M Byte" of the Intel Software Development Manual.
+ */
+ static const int regoff1[] = {
+ offsetof(struct pt_regs, bx),
+ offsetof(struct pt_regs, bx),
+ offsetof(struct pt_regs, bp),
+ offsetof(struct pt_regs, bp),
+ offsetof(struct pt_regs, si),
+ offsetof(struct pt_regs, di),
+ offsetof(struct pt_regs, bp),
+ offsetof(struct pt_regs, bx),
+ };
+
+ static const int regoff2[] = {
+ offsetof(struct pt_regs, si),
+ offsetof(struct pt_regs, di),
+ offsetof(struct pt_regs, si),
+ offsetof(struct pt_regs, di),
+ -EDOM,
+ -EDOM,
+ -EDOM,
+ -EDOM,
+ };
+
+ if (!offs1 || !offs2)
+ return -EINVAL;
+
+ /* Operand is a register, use the generic function. */
+ if (X86_MODRM_MOD(insn->modrm.value) == 3) {
+ *offs1 = insn_get_modrm_rm_off(insn, regs);
+ *offs2 = -EDOM;
+ return 0;
+ }
+
+ *offs1 = regoff1[X86_MODRM_RM(insn->modrm.value)];
+ *offs2 = regoff2[X86_MODRM_RM(insn->modrm.value)];
+
+ /*
+ * If ModRM.mod is 0 and ModRM.rm is 110b, then we use displacement-
+ * only addressing. This means that no registers are involved in
+ * computing the effective address. Thus, ensure that the first
+ * register offset is invalild. The second register offset is already
+ * invalid under the aforementioned conditions.
+ */
+ if ((X86_MODRM_MOD(insn->modrm.value) == 0) &&
+ (X86_MODRM_RM(insn->modrm.value) == 6))
+ *offs1 = -EDOM;
+
+ return 0;
+}
+
+/**
* get_desc() - Obtain pointer to a segment descriptor
* @sel: Segment selector
*
@@ -815,7 +889,9 @@ static int get_eff_addr_reg(struct insn *insn, struct pt_regs *regs,
return -EINVAL;
/* Ignore bytes that are outside the address size. */
- if (insn->addr_bytes == 4)
+ if (insn->addr_bytes == 2)
+ *eff_addr = regs_get_register(regs, *regoff) & 0xffff;
+ else if (insn->addr_bytes == 4)
*eff_addr = regs_get_register(regs, *regoff) & 0xffffffff;
else /* 64-bit address */
*eff_addr = regs_get_register(regs, *regoff);
@@ -891,6 +967,74 @@ static int get_eff_addr_modrm(struct insn *insn, struct pt_regs *regs,
}
/**
+ * get_eff_addr_modrm_16() - Obtain referenced effective address via ModRM
+ * @insn: Instruction. Must be valid.
+ * @regs: Register values as seen when entering kernel mode
+ * @regoff: Obtained operand offset, in pt_regs, associated with segment
+ * @eff_addr: Obtained effective address
+ *
+ * Obtain the 16-bit effective address referenced by the ModRM byte of @insn.
+ * After identifying the registers involved in the register-indirect memory
+ * reference, its value is obtained from the operands in @regs. The computed
+ * address is stored @eff_addr. Also, the register operand that indicates
+ * the associated segment is stored in @regoff, this parameter can later be used
+ * to determine such segment.
+ *
+ * Returns:
+ *
+ * 0 on success. @eff_addr will have the referenced effective address. @regoff
+ * will have a register, as an offset from the base of pt_regs, that can be used
+ * to resolve the associated segment.
+ *
+ * -EINVAL on error.
+ */
+static int get_eff_addr_modrm_16(struct insn *insn, struct pt_regs *regs,
+ int *regoff, short *eff_addr)
+{
+ int addr_offset1, addr_offset2, ret;
+ short addr1 = 0, addr2 = 0, displacement;
+
+ if (insn->addr_bytes != 2)
+ return -EINVAL;
+
+ insn_get_modrm(insn);
+
+ if (!insn->modrm.nbytes)
+ return -EINVAL;
+
+ if (X86_MODRM_MOD(insn->modrm.value) > 2)
+ return -EINVAL;
+
+ ret = get_reg_offset_16(insn, regs, &addr_offset1, &addr_offset2);
+ if (ret < 0)
+ return -EINVAL;
+
+ /*
+ * Don't fail on invalid offset values. They might be invalid because
+ * they cannot be used for this particular value of ModRM. Instead, use
+ * them in the computation only if they contain a valid value.
+ */
+ if (addr_offset1 != -EDOM)
+ addr1 = regs_get_register(regs, addr_offset1) & 0xffff;
+
+ if (addr_offset2 != -EDOM)
+ addr2 = regs_get_register(regs, addr_offset2) & 0xffff;
+
+ displacement = insn->displacement.value & 0xffff;
+ *eff_addr = addr1 + addr2 + displacement;
+
+ /*
+ * The first operand register could indicate to use of either SS or DS
+ * registers to obtain the segment selector. The second operand
+ * register can only indicate the use of DS. Thus, the first operand
+ * will be used to obtain the segment selector.
+ */
+ *regoff = addr_offset1;
+
+ return 0;
+}
+
+/**
* get_eff_addr_sib() - Obtain referenced effective address via SIB
* @insn: Instruction. Must be valid.
* @regs: Register values as seen when entering kernel mode
@@ -975,6 +1119,71 @@ static int get_eff_addr_sib(struct insn *insn, struct pt_regs *regs,
}
/**
+ * get_addr_ref_16() - Obtain the 16-bit address referred by instruction
+ * @insn: Instruction containing ModRM byte and displacement
+ * @regs: Register values as seen when entering kernel mode
+ *
+ * This function is to be used with 16-bit address encodings. Obtain the memory
+ * address referred by the instruction's ModRM and displacement bytes. Also, the
+ * segment used as base is determined by either any segment override prefixes in
+ * @insn or the default segment of the registers involved in the address
+ * computation. In protected mode, segment limits are enforced.
+ *
+ * Returns:
+ *
+ * Linear address referenced by the instruction operands on success.
+ *
+ * -1L on error.
+ */
+static void __user *get_addr_ref_16(struct insn *insn, struct pt_regs *regs)
+{
+ unsigned long linear_addr = -1L, seg_base, seg_limit;
+ int ret, regoff;
+ short eff_addr;
+ long tmp;
+
+ insn_get_modrm(insn);
+ insn_get_displacement(insn);
+
+ if (insn->addr_bytes != 2)
+ goto out;
+
+ if (X86_MODRM_MOD(insn->modrm.value) == 3) {
+ ret = get_eff_addr_reg(insn, regs, &regoff, &tmp);
+ if (ret)
+ goto out;
+
+ eff_addr = tmp;
+ } else {
+ ret = get_eff_addr_modrm_16(insn, regs, &regoff, &eff_addr);
+ if (ret)
+ goto out;
+ }
+
+ ret = get_seg_base_limit(insn, regs, regoff, &seg_base, &seg_limit);
+ if (ret)
+ goto out;
+
+ /*
+ * Before computing the linear address, make sure the effective address
+ * is within the limits of the segment. In virtual-8086 mode, segment
+ * limits are not enforced. In such a case, the segment limit is -1L to
+ * reflect this fact.
+ */
+ if ((unsigned long)(eff_addr & 0xffff) > seg_limit)
+ goto out;
+
+ 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;
+}
+
+/**
* get_addr_ref_32() - Obtain a 32-bit linear address
* @insn: Instruction with ModRM, SIB bytes and displacement
* @regs: Register values as seen when entering kernel mode
@@ -1143,6 +1352,8 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
return (void __user *)-1L;
switch (insn->addr_bytes) {
+ case 2:
+ return get_addr_ref_16(insn, regs);
case 4:
return get_addr_ref_32(insn, regs);
case 8: