linux-kernel - [PATCH v7 14/26] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 5

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Date:   Fri,  5 May 2017 11:17:12 -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>,
        Alexandre Julliard <julliard@...ehq.org>,
        Stas Sergeev <stsp@...t.ru>, Fenghua Yu <fenghua.yu@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-msdos@...r.kernel.org, wine-devel@...ehq.org,
        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>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: [PATCH v7 14/26] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 5

Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software
Developer's Manual volume 2A states that when ModRM.mod is zero and
ModRM.rm is 101b, a 32-bit displacement follows the ModRM byte. This means
that none of the registers are used in the computation of the effective
address. A return value of -EDOM signals callers that they should not use
the value of registers when computing the effective address for the
instruction.

In IA-32e 64-bit mode (long mode), the effective address is given by the
32-bit displacement plus the value of RIP of the next instruction.
In IA-32e compatibility mode (protected mode), only the displacement is
used.

The instruction decoder takes care of obtaining the displacement.

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: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Thomas Garnier <thgarnie@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: Dmitry Vyukov <dvyukov@...gle.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/lib/insn-eval.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 693e5a8..4f600de 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -379,6 +379,12 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
 	switch (type) {
 	case REG_TYPE_RM:
 		regno = X86_MODRM_RM(insn->modrm.value);
+		/*
+		 * ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit displacement
+		 * follows the ModRM byte.
+		 */
+		if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5)
+			return -EDOM;
 		if (X86_REX_B(insn->rex_prefix.value))
 			regno += 8;
 		break;
@@ -730,9 +736,21 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
 			eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
 		} else {
 			addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
-			if (addr_offset < 0)
+			/*
+			 * -EDOM means that we must ignore the address_offset.
+			 * In such a case, in 64-bit mode the effective address
+			 * relative to the RIP of the following instruction.
+			 */
+			if (addr_offset == -EDOM) {
+				eff_addr = 0;
+				if (user_64bit_mode(regs))
+					eff_addr = (long)regs->ip +
+						   insn->length;
+			} else if (addr_offset < 0) {
 				goto out_err;
-			eff_addr = regs_get_register(regs, addr_offset);
+			} else {
+				eff_addr = regs_get_register(regs, addr_offset);
+			}
 		}
 		eff_addr += insn->displacement.value;
 	}
-- 
2.9.3