[v5 03/20] x86/mpx: Do not use R/EBP as base in the SIB byte with Mod = 0

2017-03-03 Thread Ricardo Neri 
Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software
Developer's Manual volume 2A states that when a SIB byte is used and the
base of the SIB byte points to R/EBP (i.e., base = 5) and the mod part
of the ModRM byte is zero, the value of such register will not be used
as part of the address computation. To signal this, a -EDOM error is
returned to indicate callers that they should ignore the value.

Also, for this particular case, a displacement of 32-bits should follow
the SIB byte if the mod part of ModRM is equal to zero. The instruction
decoder ensures that this is the case.

Cc: Dave Hansen 
Cc: Adam Buchbinder 
Cc: Colin Ian King 
Cc: Lorenzo Stoakes 
Cc: Qiaowei Ren 
Cc: Peter Zijlstra 
Cc: Nathan Howard 
Cc: Adan Hawthorn 
Cc: Joe Perches 
Cc: Ravi V. Shankar 
Cc: x...@kernel.org
Signed-off-by: Ricardo Neri 
---
 arch/x86/mm/mpx.c | 29 ++---
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index d9e92d6..ef7eb67 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -121,6 +121,17 @@ static int get_reg_offset(struct insn *insn, struct 
pt_regs *regs,
 
case REG_TYPE_BASE:
regno = X86_SIB_BASE(insn->sib.value);
+   /*
+* If mod is 0 and register R/EBP (regno=5) is indicated in the
+* base part of the SIB byte, the value of such register should
+* not be used in the address computation. Also, a 32-bit
+* displacement is expected in this case; the instruction
+* decoder takes care of it. This is true for both R13 and
+* R/EBP as REX.B will not be decoded.
+*/
+   if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
+   return -EDOM;
+
if (X86_REX_B(insn->rex_prefix.value))
regno += 8;
break;
@@ -161,16 +172,21 @@ static void __user *mpx_get_addr_ref(struct insn *insn, 
struct pt_regs *regs)
eff_addr = regs_get_register(regs, addr_offset);
} else {
if (insn->sib.nbytes) {
+   /*
+* Negative values in the base and index offset means
+* an error when decoding the SIB byte. Except -EDOM,
+* which means that the registers should not be used
+* in the address computation.
+*/
base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
-   if (base_offset < 0)
+   if (unlikely(base_offset == -EDOM))
+   base = 0;
+   else if (unlikely(base_offset < 0))
goto out_err;
+   else
+   base = regs_get_register(regs, base_offset);
 
indx_offset = get_reg_offset(insn, regs, 
REG_TYPE_INDEX);
-   /*
-* A negative offset generally means a error, except
-* -EDOM, which means that the contents of the register
-* should not be used as index.
-*/
if (unlikely(indx_offset == -EDOM))
indx = 0;
else if (unlikely(indx_offset < 0))
@@ -178,7 +194,6 @@ static void __user *mpx_get_addr_ref(struct insn *insn, 
struct pt_regs *regs)
else
indx = regs_get_register(regs, indx_offset);
 
-   base = regs_get_register(regs, base_offset);
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
-- 
2.9.3

[v5 03/20] x86/mpx: Do not use R/EBP as base in the SIB byte with Mod = 0

2017-03-03 Thread Ricardo Neri 
Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software
Developer's Manual volume 2A states that when a SIB byte is used and the
base of the SIB byte points to R/EBP (i.e., base = 5) and the mod part
of the ModRM byte is zero, the value of such register will not be used
as part of the address computation. To signal this, a -EDOM error is
returned to indicate callers that they should ignore the value.

Also, for this particular case, a displacement of 32-bits should follow
the SIB byte if the mod part of ModRM is equal to zero. The instruction
decoder ensures that this is the case.

Cc: Dave Hansen 
Cc: Adam Buchbinder 
Cc: Colin Ian King 
Cc: Lorenzo Stoakes 
Cc: Qiaowei Ren 
Cc: Peter Zijlstra 
Cc: Nathan Howard 
Cc: Adan Hawthorn 
Cc: Joe Perches 
Cc: Ravi V. Shankar 
Cc: x...@kernel.org
Signed-off-by: Ricardo Neri 
---
 arch/x86/mm/mpx.c | 29 ++---
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index d9e92d6..ef7eb67 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -121,6 +121,17 @@ static int get_reg_offset(struct insn *insn, struct 
pt_regs *regs,
 
case REG_TYPE_BASE:
regno = X86_SIB_BASE(insn->sib.value);
+   /*
+* If mod is 0 and register R/EBP (regno=5) is indicated in the
+* base part of the SIB byte, the value of such register should
+* not be used in the address computation. Also, a 32-bit
+* displacement is expected in this case; the instruction
+* decoder takes care of it. This is true for both R13 and
+* R/EBP as REX.B will not be decoded.
+*/
+   if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
+   return -EDOM;
+
if (X86_REX_B(insn->rex_prefix.value))
regno += 8;
break;
@@ -161,16 +172,21 @@ static void __user *mpx_get_addr_ref(struct insn *insn, 
struct pt_regs *regs)
eff_addr = regs_get_register(regs, addr_offset);
} else {
if (insn->sib.nbytes) {
+   /*
+* Negative values in the base and index offset means
+* an error when decoding the SIB byte. Except -EDOM,
+* which means that the registers should not be used
+* in the address computation.
+*/
base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
-   if (base_offset < 0)
+   if (unlikely(base_offset == -EDOM))
+   base = 0;
+   else if (unlikely(base_offset < 0))
goto out_err;
+   else
+   base = regs_get_register(regs, base_offset);
 
indx_offset = get_reg_offset(insn, regs, 
REG_TYPE_INDEX);
-   /*
-* A negative offset generally means a error, except
-* -EDOM, which means that the contents of the register
-* should not be used as index.
-*/
if (unlikely(indx_offset == -EDOM))
indx = 0;
else if (unlikely(indx_offset < 0))
@@ -178,7 +194,6 @@ static void __user *mpx_get_addr_ref(struct insn *insn, 
struct pt_regs *regs)
else
indx = regs_get_register(regs, indx_offset);
 
-   base = regs_get_register(regs, base_offset);
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
-- 
2.9.3