diff mbox series

[-tip,v2,1/2] x86: xen: insn: Decode Xen and KVM emulate-prefix signature

Message ID 156773101914.29031.4027232648773934988.stgit@devnote2
State Superseded
Headers show
Series x86: kprobes: Prohibit kprobes on Xen/KVM emulate prefixes | expand

Commit Message

Masami Hiramatsu Sept. 6, 2019, 12:50 a.m. UTC
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.

Reported-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v2:
  - Generalize the emulate-prefix handling not only for Xen but KVM.
  - Introduce insn.emulate_prefix_size instead of using insn.prefixes.
---
 arch/x86/include/asm/insn.h             |    6 +++++
 arch/x86/include/asm/xen/interface.h    |    7 ++++--
 arch/x86/include/asm/xen/prefix.h       |   10 +++++++++
 arch/x86/lib/insn.c                     |   36 +++++++++++++++++++++++++++++++
 tools/arch/x86/include/asm/insn.h       |    6 +++++
 tools/arch/x86/include/asm/xen/prefix.h |   10 +++++++++
 tools/arch/x86/lib/insn.c               |   36 +++++++++++++++++++++++++++++++
 tools/objtool/sync-check.sh             |    3 ++-
 8 files changed, 111 insertions(+), 3 deletions(-)
 create mode 100644 arch/x86/include/asm/xen/prefix.h
 create mode 100644 tools/arch/x86/include/asm/xen/prefix.h

Comments

Josh Poimboeuf Sept. 6, 2019, 1:13 a.m. UTC | #1
On Fri, Sep 06, 2019 at 09:50:19AM +0900, Masami Hiramatsu wrote:
> --- 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/xen/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/xen/prefix.h[\">]"'

Unfortunately perf also has a similar sync check script:
tools/perf/check-headers.sh.  So you'll also need to add the above
changes there.

Otherwise

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Masami Hiramatsu Sept. 6, 2019, 1:39 a.m. UTC | #2
On Thu, 5 Sep 2019 20:13:50 -0500
Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> On Fri, Sep 06, 2019 at 09:50:19AM +0900, Masami Hiramatsu wrote:
> > --- 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/xen/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/xen/prefix.h[\">]"'
> 
> Unfortunately perf also has a similar sync check script:
> tools/perf/check-headers.sh.  So you'll also need to add the above
> changes there.

Oops, I thought it was integrated... OK, I'll update this patch.

> 
> Otherwise
> 
> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

Thanks!

> 
> -- 
> Josh
diff mbox series

Patch

diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h
index 154f27be8bfc..5c1ae3eff9d4 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/include/asm/xen/interface.h b/arch/x86/include/asm/xen/interface.h
index 62ca03ef5c65..fe33a9798708 100644
--- a/arch/x86/include/asm/xen/interface.h
+++ b/arch/x86/include/asm/xen/interface.h
@@ -379,12 +379,15 @@  struct xen_pmu_arch {
  * Prefix forces emulation of some non-trapping instructions.
  * Currently only CPUID.
  */
+#include <asm/xen/prefix.h>
+
 #ifdef __ASSEMBLY__
-#define XEN_EMULATE_PREFIX .byte 0x0f,0x0b,0x78,0x65,0x6e ;
+#define XEN_EMULATE_PREFIX .byte __XEN_EMULATE_PREFIX ;
 #define XEN_CPUID          XEN_EMULATE_PREFIX cpuid
 #else
-#define XEN_EMULATE_PREFIX ".byte 0x0f,0x0b,0x78,0x65,0x6e ; "
+#define XEN_EMULATE_PREFIX ".byte " __XEN_EMULATE_PREFIX_STR " ; "
 #define XEN_CPUID          XEN_EMULATE_PREFIX "cpuid"
+
 #endif
 
 #endif /* _ASM_X86_XEN_INTERFACE_H */
diff --git a/arch/x86/include/asm/xen/prefix.h b/arch/x86/include/asm/xen/prefix.h
new file mode 100644
index 000000000000..f901be0d7a95
--- /dev/null
+++ b/arch/x86/include/asm/xen/prefix.h
@@ -0,0 +1,10 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _TOOLS_ASM_X86_XEN_PREFIX_H
+#define _TOOLS_ASM_X86_XEN_PREFIX_H
+
+#include <linux/stringify.h>
+
+#define __XEN_EMULATE_PREFIX  0x0f,0x0b,0x78,0x65,0x6e
+#define __XEN_EMULATE_PREFIX_STR  __stringify(__XEN_EMULATE_PREFIX)
+
+#endif
diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 0b5862ba6a75..b7eb50187db9 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -13,6 +13,9 @@ 
 #include <asm/inat.h>
 #include <asm/insn.h>
 
+/* For special Xen prefix */
+#include <asm/xen/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 +61,37 @@  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 };
+/* See handle_ud()@arch/x86/kvm/x86.c */
+static const insn_byte_t kvm_prefix[] = "\xf\xbkvm";
+
+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 +110,8 @@  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/insn.h b/tools/arch/x86/include/asm/insn.h
index 37a4c390750b..568854b14d0a 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/include/asm/xen/prefix.h b/tools/arch/x86/include/asm/xen/prefix.h
new file mode 100644
index 000000000000..f901be0d7a95
--- /dev/null
+++ b/tools/arch/x86/include/asm/xen/prefix.h
@@ -0,0 +1,10 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _TOOLS_ASM_X86_XEN_PREFIX_H
+#define _TOOLS_ASM_X86_XEN_PREFIX_H
+
+#include <linux/stringify.h>
+
+#define __XEN_EMULATE_PREFIX  0x0f,0x0b,0x78,0x65,0x6e
+#define __XEN_EMULATE_PREFIX_STR  __stringify(__XEN_EMULATE_PREFIX)
+
+#endif
diff --git a/tools/arch/x86/lib/insn.c b/tools/arch/x86/lib/insn.c
index 79e048f1d902..ce04e43e0749 100644
--- a/tools/arch/x86/lib/insn.c
+++ b/tools/arch/x86/lib/insn.c
@@ -13,6 +13,9 @@ 
 #include "../include/asm/inat.h"
 #include "../include/asm/insn.h"
 
+/* For special Xen prefix */
+#include "../include/asm/xen/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 +61,37 @@  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 };
+/* See handle_ud()@arch/x86/kvm/x86.c */
+static const insn_byte_t kvm_prefix[] = "\xf\xbkvm";
+
+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 +110,8 @@  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 0a832e265a50..34143ea3d477 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/xen/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/xen/prefix.h[\">]"'
 
 cd -