[PATCH v9 06/29] x86/mpx: Use signed variables to compute effective addresses

[Ricardo Neri]

Even though memory addresses are unsigned, the operands used to compute the
effective address do have a sign. This is true for ModRM.rm, SIB.base,
SIB.index as well as the displacement bytes. Thus, signed variables shall
be used when computing the effective address from these operands. Once the
signed effective address has been computed, it is casted to an unsigned
long to determine the linear address.

Variables are renamed to better reflect the type of address being
computed.

Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Adam Buchbinder <adam.buchbinder@xxxxxxxxx>
Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Qiaowei Ren <qiaowei.ren@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Nathan Howard <liverlint@xxxxxxxxx>
Cc: Adan Hawthorn <adanhawthorn@xxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 arch/x86/mm/mpx.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index f4c48a0..57e5bf5 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -138,8 +138,9 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
  */
 static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 {
-	unsigned long addr = -1L, base, indx;
 	int addr_offset, base_offset, indx_offset;
+	unsigned long linear_addr = -1L;
+	long eff_addr, base, indx;
 	insn_byte_t sib;
 
 	insn_get_modrm(insn);
@@ -150,7 +151,8 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 		addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
 		if (addr_offset < 0)
 			goto out;
-		addr = regs_get_register(regs, addr_offset);
+
+		eff_addr = regs_get_register(regs, addr_offset);
 	} else {
 		if (insn->sib.nbytes) {
 			base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
@@ -163,17 +165,23 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 
 			base = regs_get_register(regs, base_offset);
 			indx = regs_get_register(regs, indx_offset);
-			addr = base + indx * (1 << X86_SIB_SCALE(sib));
+
+			eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
 		} else {
 			addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
 			if (addr_offset < 0)
 				goto out;
-			addr = regs_get_register(regs, addr_offset);
+
+			eff_addr = regs_get_register(regs, addr_offset);
 		}
-		addr += insn->displacement.value;
+
+		eff_addr += insn->displacement.value;
 	}
+
+	linear_addr = (unsigned long)eff_addr;
+
 out:
-	return (void __user *)addr;
+	return (void __user *)linear_addr;
 }
 
 static int mpx_insn_decode(struct insn *insn,
-- 
2.7.4