linux-kernel - [PATCH 2/4] [BUGFIX] x86: Fix instruction decoder to handle grouped AVX instructions

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Date:	Tue, 22 Nov 2011 03:11:11 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org, yrl.pp-manager.tt@...achi.com
Subject: [PATCH 2/4] [BUGFIX] x86: Fix instruction decoder to handle grouped
 AVX instructions

For reducing memory usage of attribute table, x86 instruction
decoder puts "Group" attribute only on "no-last-prefix"
attribute table (same as vex_p == 0 case).

Thus, the decoder should look no-last-prefix table first, and
then only if it is not a group, move on to "with-last-prefix"
table (vex_p != 0).

However, current implementation, inat_get_avx_attribute()
looks with-last-prefix directly. So, when decoding
a grouped AVX instruction, the decoder fails to find correct
group because there is no "Group" attribute on the table.
This ends up with the mis-decoding of instructions, as Ingo
reported in http://thread.gmane.org/gmane.linux.kernel/1214103


This patch fixes it to check no-last-prefix table first
even if that is an AVX instruction, and get an attribute from
"with last-prefix" table only if that is not a group.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Reported-by: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
---
 arch/x86/lib/inat.c |    9 ++++++++-
 arch/x86/lib/insn.c |    4 +++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/inat.c b/arch/x86/lib/inat.c
index 46fc4ee..88ad5fb 100644
--- a/arch/x86/lib/inat.c
+++ b/arch/x86/lib/inat.c
@@ -82,9 +82,16 @@ insn_attr_t inat_get_avx_attribute(insn_byte_t opcode, insn_byte_t vex_m,
 	const insn_attr_t *table;
 	if (vex_m > X86_VEX_M_MAX || vex_p > INAT_LSTPFX_MAX)
 		return 0;
-	table = inat_avx_tables[vex_m][vex_p];
+	/* At first, this checks the master table */
+	table = inat_avx_tables[vex_m][0];
 	if (!table)
 		return 0;
+	if (!inat_is_group(table[opcode]) && vex_p) {
+		/* If this is not a group, get attribute directly */
+		table = inat_avx_tables[vex_m][vex_p];
+		if (!table)
+			return 0;
+	}
 	return table[opcode];
 }
 
diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 374562e..5a1f9f3 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -202,7 +202,7 @@ void insn_get_opcode(struct insn *insn)
 		m = insn_vex_m_bits(insn);
 		p = insn_vex_p_bits(insn);
 		insn->attr = inat_get_avx_attribute(op, m, p);
-		if (!inat_accept_vex(insn->attr))
+		if (!inat_accept_vex(insn->attr) && !inat_is_group(insn->attr))
 			insn->attr = 0;	/* This instruction is bad */
 		goto end;	/* VEX has only 1 byte for opcode */
 	}
@@ -249,6 +249,8 @@ void insn_get_modrm(struct insn *insn)
 			pfx = insn_last_prefix(insn);
 			insn->attr = inat_get_group_attribute(mod, pfx,
 							      insn->attr);
+			if (insn_is_avx(insn) && !inat_accept_vex(insn->attr))
+				insn->attr = 0;	/* This is bad */
 		}
 	}
 

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