[PATCH v7 03/26] 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 the 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 
Cc: Andy Lutomirski 
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: [e-mail]
Signed-off-by: Ricardo Neri 
---
 arch/x86/mm/mpx.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 1c34b76..ebdead8 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -138,7 +138,8 @@ 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, base, indx;
+	unsigned long linear_addr;
+	long eff_addr, base, indx;
    int addr_offset, base_offset, indx_offset;
    insn_byte_t sib;

@@ -150,7 +151,7 @@ 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_err;
-		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);
@@ -163,16 +164,18 @@ 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_err;
-			addr = regs_get_register(regs, addr_offset);
+			eff_addr = regs_get_register(regs, addr_offset);
    	}
-		addr += insn->displacement.value;
+		eff_addr += insn->displacement.value;
    }
-	return (void __user *)addr;
+	linear_addr = (unsigned long)eff_addr;
+
+	return (void __user *)linear_addr;
 out_err:
    return (void __user *)-1;
 }