Commit 130b78b2 authored Dec 05, 2011 by Masami Hiramatsu Committed by Ingo Molnar Dec 05, 2011

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.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: yrl.pp-manager.tt@hitachi.com
Link: http://lkml.kernel.org/r/20111205120539.15475.91428.stgit@cloud


Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 1056c3e9

arch/x86/lib/inat.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -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;
		/* 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];
		}

arch/x86/lib/insn.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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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