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x86/insn-eval: Add support to resolve 16-bit address encodings

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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>
This commit is contained in:
Ricardo Neri 2017-11-05 18:27:50 -08:00 committed by Ingo Molnar
parent 86cc351090
commit 9c6c799fae
1 changed files with 212 additions and 1 deletions
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213
arch/x86/lib/insn-eval.c
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@ -480,6 +480,80 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
return regoff[regno];
}
/**
* 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);
@ -890,6 +966,74 @@ static int get_eff_addr_modrm(struct insn *insn, struct pt_regs *regs,
return 0;
}
/**
* 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.
@ -974,6 +1118,71 @@ static int get_eff_addr_sib(struct insn *insn, struct pt_regs *regs,
return 0;
}
/**
* 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
@ -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: