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x86: xen: insn: Decode Xen and KVM emulate-prefix signature

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Decode Xen and KVM's emulate-prefix signature by x86 insn decoder.
It is called "prefix" but actually not x86 instruction prefix, so
this adds insn.emulate_prefix_size field instead of reusing
insn.prefixes.

If x86 decoder finds a special sequence of instructions of
XEN_EMULATE_PREFIX and 'ud2a; .ascii "kvm"', it just counts the
length, set insn.emulate_prefix_size and fold it with the next
instruction. In other words, the signature and the next instruction
is treated as a single instruction.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: x86@kernel.org
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: xen-devel@lists.xenproject.org
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: https://lkml.kernel.org/r/156777564986.25081.4964537658500952557.stgit@devnote2
This commit is contained in:
Masami Hiramatsu 2019-09-06 22:14:10 +09:00 committed by Peter Zijlstra
parent b3dc0695fa
commit 4d65adfcd1
7 changed files with 98 additions and 2 deletions
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6
arch/x86/include/asm/insn.h
View File

@ -45,6 +45,7 @@ struct insn {
struct insn_field immediate2; /* for 64bit imm or seg16 */
};
int emulate_prefix_size;
insn_attr_t attr;
unsigned char opnd_bytes;
unsigned char addr_bytes;
@ -128,6 +129,11 @@ static inline int insn_is_evex(struct insn *insn)
return (insn->vex_prefix.nbytes == 4);
}
static inline int insn_has_emulate_prefix(struct insn *insn)
{
return !!insn->emulate_prefix_size;
}
/* Ensure this instruction is decoded completely */
static inline int insn_complete(struct insn *insn)
{

34
arch/x86/lib/insn.c
View File

@ -13,6 +13,8 @@
#include <asm/inat.h>
#include <asm/insn.h>
#include <asm/emulate_prefix.h>
/* Verify next sizeof(t) bytes can be on the same instruction */
#define validate_next(t, insn, n) \
((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)
@ -58,6 +60,36 @@ void insn_init(struct insn *insn, const void *kaddr, int buf_len, int x86_64)
insn->addr_bytes = 4;
}
static const insn_byte_t xen_prefix[] = { __XEN_EMULATE_PREFIX };
static const insn_byte_t kvm_prefix[] = { __KVM_EMULATE_PREFIX };
static int __insn_get_emulate_prefix(struct insn *insn,
const insn_byte_t *prefix, size_t len)
{
size_t i;
for (i = 0; i < len; i++) {
if (peek_nbyte_next(insn_byte_t, insn, i) != prefix[i])
goto err_out;
}
insn->emulate_prefix_size = len;
insn->next_byte += len;
return 1;
err_out:
return 0;
}
static void insn_get_emulate_prefix(struct insn *insn)
{
if (__insn_get_emulate_prefix(insn, xen_prefix, sizeof(xen_prefix)))
return;
__insn_get_emulate_prefix(insn, kvm_prefix, sizeof(kvm_prefix));
}
/**
* insn_get_prefixes - scan x86 instruction prefix bytes
* @insn: &struct insn containing instruction
@ -76,6 +108,8 @@ void insn_get_prefixes(struct insn *insn)
if (prefixes->got)
return;
insn_get_emulate_prefix(insn);
nb = 0;
lb = 0;
b = peek_next(insn_byte_t, insn);

14
tools/arch/x86/include/asm/emulate_prefix.h Normal file
View File

@ -0,0 +1,14 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_X86_EMULATE_PREFIX_H
#define _ASM_X86_EMULATE_PREFIX_H
/*
* Virt escape sequences to trigger instruction emulation;
* ideally these would decode to 'whole' instruction and not destroy
* the instruction stream; sadly this is not true for the 'kvm' one :/
*/
#define __XEN_EMULATE_PREFIX 0x0f,0x0b,0x78,0x65,0x6e /* ud2 ; .ascii "xen" */
#define __KVM_EMULATE_PREFIX 0x0f,0x0b,0x6b,0x76,0x6d /* ud2 ; .ascii "kvm" */
#endif

6
tools/arch/x86/include/asm/insn.h
View File

@ -45,6 +45,7 @@ struct insn {
struct insn_field immediate2; /* for 64bit imm or seg16 */
};
int emulate_prefix_size;
insn_attr_t attr;
unsigned char opnd_bytes;
unsigned char addr_bytes;
@ -128,6 +129,11 @@ static inline int insn_is_evex(struct insn *insn)
return (insn->vex_prefix.nbytes == 4);
}
static inline int insn_has_emulate_prefix(struct insn *insn)
{
return !!insn->emulate_prefix_size;
}
/* Ensure this instruction is decoded completely */
static inline int insn_complete(struct insn *insn)
{

34
tools/arch/x86/lib/insn.c
View File

@ -13,6 +13,8 @@
#include "../include/asm/inat.h"
#include "../include/asm/insn.h"
#include "../include/asm/emulate_prefix.h"
/* Verify next sizeof(t) bytes can be on the same instruction */
#define validate_next(t, insn, n) \
((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)
@ -58,6 +60,36 @@ void insn_init(struct insn *insn, const void *kaddr, int buf_len, int x86_64)
insn->addr_bytes = 4;
}
static const insn_byte_t xen_prefix[] = { __XEN_EMULATE_PREFIX };
static const insn_byte_t kvm_prefix[] = { __KVM_EMULATE_PREFIX };
static int __insn_get_emulate_prefix(struct insn *insn,
const insn_byte_t *prefix, size_t len)
{
size_t i;
for (i = 0; i < len; i++) {
if (peek_nbyte_next(insn_byte_t, insn, i) != prefix[i])
goto err_out;
}
insn->emulate_prefix_size = len;
insn->next_byte += len;
return 1;
err_out:
return 0;
}
static void insn_get_emulate_prefix(struct insn *insn)
{
if (__insn_get_emulate_prefix(insn, xen_prefix, sizeof(xen_prefix)))
return;
__insn_get_emulate_prefix(insn, kvm_prefix, sizeof(kvm_prefix));
}
/**
* insn_get_prefixes - scan x86 instruction prefix bytes
* @insn: &struct insn containing instruction
@ -76,6 +108,8 @@ void insn_get_prefixes(struct insn *insn)
if (prefixes->got)
return;
insn_get_emulate_prefix(insn);
nb = 0;
lb = 0;
b = peek_next(insn_byte_t, insn);

3
tools/objtool/sync-check.sh
View File

@ -4,6 +4,7 @@
FILES='
arch/x86/include/asm/inat_types.h
arch/x86/include/asm/orc_types.h
arch/x86/include/asm/emulate_prefix.h
arch/x86/lib/x86-opcode-map.txt
arch/x86/tools/gen-insn-attr-x86.awk
'
@ -46,6 +47,6 @@ done
check arch/x86/include/asm/inat.h '-I "^#include [\"<]\(asm/\)*inat_types.h[\">]"'
check arch/x86/include/asm/insn.h '-I "^#include [\"<]\(asm/\)*inat.h[\">]"'
check arch/x86/lib/inat.c '-I "^#include [\"<]\(../include/\)*asm/insn.h[\">]"'
check arch/x86/lib/insn.c '-I "^#include [\"<]\(../include/\)*asm/in\(at\|sn\).h[\">]"'
check arch/x86/lib/insn.c '-I "^#include [\"<]\(../include/\)*asm/in\(at\|sn\).h[\">]" -I "^#include [\"<]\(../include/\)*asm/emulate_prefix.h[\">]"'
cd -

3
tools/perf/check-headers.sh
View File

@ -28,6 +28,7 @@ arch/x86/include/asm/disabled-features.h
arch/x86/include/asm/required-features.h
arch/x86/include/asm/cpufeatures.h
arch/x86/include/asm/inat_types.h
arch/x86/include/asm/emulate_prefix.h
arch/x86/include/uapi/asm/prctl.h
arch/x86/lib/x86-opcode-map.txt
arch/x86/tools/gen-insn-attr-x86.awk
@ -116,7 +117,7 @@ check lib/ctype.c '-I "^EXPORT_SYMBOL" -I "^#include <linux/export.h>" -B
check arch/x86/include/asm/inat.h '-I "^#include [\"<]\(asm/\)*inat_types.h[\">]"'
check arch/x86/include/asm/insn.h '-I "^#include [\"<]\(asm/\)*inat.h[\">]"'
check arch/x86/lib/inat.c '-I "^#include [\"<]\(../include/\)*asm/insn.h[\">]"'
check arch/x86/lib/insn.c '-I "^#include [\"<]\(../include/\)*asm/in\(at\|sn\).h[\">]"'
check arch/x86/lib/insn.c '-I "^#include [\"<]\(../include/\)*asm/in\(at\|sn\).h[\">]" -I "^#include [\"<]\(../include/\)*asm/emulate_prefix.h[\">]"'
# diff non-symmetric files
check_2 tools/perf/arch/x86/entry/syscalls/syscall_64.tbl arch/x86/entry/syscalls/syscall_64.tbl