[PATCH 3/4] x86: xen: insn: Decode Xen and KVM emulate-prefix signature - Linux-stable-mirror

10 May 2022

From: Masami Hiramatsu mhiramat@kernel.org
commit 4d65adfcd1196818659d3bd9b42dccab291e1751 upstream
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@devno...
[mheyne: resolved contextual conflict in tools/objtools/sync-check.sh]
Signed-off-by: Maximilian Heyne mheyne@amazon.de
Cc: stable@vger.kernel.org # 5.4.x
---
 arch/x86/include/asm/insn.h                 |  6 ++++
 arch/x86/lib/insn.c                         | 34 +++++++++++++++++++++
 tools/arch/x86/include/asm/emulate_prefix.h | 14 +++++++++
 tools/arch/x86/include/asm/insn.h           |  6 ++++
 tools/arch/x86/lib/insn.c                   | 34 +++++++++++++++++++++
 tools/objtool/sync-check.sh                 |  3 +-
 tools/perf/check-headers.sh                 |  3 +-
 7 files changed, 98 insertions(+), 2 deletions(-)
 create mode 100644 tools/arch/x86/include/asm/emulate_prefix.h

diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h
index a51ffeea6d87..a8c3d284fa46 100644
--- a/arch/x86/include/asm/insn.h
+++ b/arch/x86/include/asm/insn.h
@@ -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)
 {
diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 0b5862ba6a75..404279563891 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -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);
diff --git a/tools/arch/x86/include/asm/emulate_prefix.h b/tools/arch/x86/include/asm/emulate_prefix.h
new file mode 100644
index 000000000000..70f5b98a5286
--- /dev/null
+++ b/tools/arch/x86/include/asm/emulate_prefix.h
@@ -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
diff --git a/tools/arch/x86/include/asm/insn.h b/tools/arch/x86/include/asm/insn.h
index d7f0ae8f3c44..52c6262e6bfd 100644
--- a/tools/arch/x86/include/asm/insn.h
+++ b/tools/arch/x86/include/asm/insn.h
@@ -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)
 {
diff --git a/tools/arch/x86/lib/insn.c b/tools/arch/x86/lib/insn.c
index 79e048f1d902..0151dfc6da61 100644
--- a/tools/arch/x86/lib/insn.c
+++ b/tools/arch/x86/lib/insn.c
@@ -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);
diff --git a/tools/objtool/sync-check.sh b/tools/objtool/sync-check.sh
index c3ae1e8ae119..2a1261bfbb62 100755
--- a/tools/objtool/sync-check.sh
+++ b/tools/objtool/sync-check.sh
@@ -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
 '
@@ -46,4 +47,4 @@ 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[">]"'
diff --git a/tools/perf/check-headers.sh b/tools/perf/check-headers.sh
index cea13cb987d0..499235a41162 100755
--- a/tools/perf/check-headers.sh
+++ b/tools/perf/check-headers.sh
@@ -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
-- 
2.32.0




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