[tip:x86/mpx] x86/mpx: Use signed variables to compute effective addresses

[tip-bot for Ricardo Neri]

Commit-ID:  b8d2eff3b1c6e46238a5fb3f56843e9974b4889f
Gitweb:     https://git.kernel.org/tip/b8d2eff3b1c6e46238a5fb3f56843e9974b4889f
Author:     Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
AuthorDate: Fri, 27 Oct 2017 13:25:33 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 1 Nov 2017 21:50:09 +0100

x86/mpx: Use signed variables to compute effective addresses

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.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Cc: Adan Hawthorn <adanhawthorn@xxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: ricardo.neri@xxxxxxxxx
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>
Cc: Qiaowei Ren <qiaowei.ren@xxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Cc: Nathan Howard <liverlint@xxxxxxxxx>
Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Cc: Chen Yucong <slaoub@xxxxxxxxx>
Cc: Adam Buchbinder <adam.buchbinder@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/1509135945-13762-7-git-send-email-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,