linux-kernel - [PATCH v8 05/28] x86/mpx: Use signed variables to compute effective addresses

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Message-Id: <20170819002809.111312-6-ricardo.neri-calderon@linux.intel.com>
Date:   Fri, 18 Aug 2017 17:27:46 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Liang Z Li <liang.z.li@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, ricardo.neri@...el.com,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Adam Buchbinder <adam.buchbinder@...il.com>,
        Colin Ian King <colin.king@...onical.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Qiaowei Ren <qiaowei.ren@...el.com>,
        Nathan Howard <liverlint@...il.com>,
        Adan Hawthorn <adanhawthorn@...il.com>,
        Joe Perches <joe@...ches.com>
Subject: [PATCH v8 05/28] 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.

Cc: Borislav Petkov <bp@...e.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Adam Buchbinder <adam.buchbinder@...il.com>
Cc: Colin Ian King <colin.king@...onical.com>
Cc: Lorenzo Stoakes <lstoakes@...il.com>
Cc: Qiaowei Ren <qiaowei.ren@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Nathan Howard <liverlint@...il.com>
Cc: Adan Hawthorn <adanhawthorn@...il.com>
Cc: Joe Perches <joe@...ches.com>
Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
Cc: x86@...nel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
 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 9ceaa955d2ba..9eec98022510 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, base, indx;
 	int addr_offset, base_offset, indx_offset;
+	unsigned long linear_addr;
+	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_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 +165,22 @@ 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;
 }
-- 
2.13.0