From: Masami Hiramatsu <mhiramat@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
Linux Next Mailing List <linux-next@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>
Subject: Re: linux-next: Tree for Aug 27 (objtool)
Date: Thu, 29 Aug 2019 10:53:56 +0900 [thread overview]
Message-ID: <20190829105356.1fd4859f49c142945146855f@kernel.org> (raw)
In-Reply-To: <20190828163433.4ltoxmtuujkqspar@treble>
[-- Attachment #1: Type: text/plain, Size: 1760 bytes --]
Hi Josh,
On Wed, 28 Aug 2019 11:34:33 -0500
Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Wed, Aug 28, 2019 at 11:13:31AM -0500, Josh Poimboeuf wrote:
> > Turns out this patch does break something:
> >
> > arch/x86/xen/enlighten_pv.o: warning: objtool: xen_cpuid()+0x25: can't find jump dest instruction at .text+0x9c
> >
> > I'll need to figure out a better way to whitelist that
> > XEN_EMULATE_PREFIX fake instruction thing. I'll probably just teach
> > the objtool decoder about it.
>
> Hi Masami,
>
> Is it possible for the kernel x86 decoder to recognize the
> XEN_EMULATE_PREFIX prefix?
>
> asm(XEN_EMULATE_PREFIX "cpuid"
> : "=a" (*ax),
> "=b" (*bx),
> "=c" (*cx),
> "=d" (*dx)
> : "0" (*ax), "2" (*cx));
>
> is disassembled to:
>
> 33: 0f 0b ud2
> 35: 78 65 js 9c <xen_store_tr+0xc>
> 37: 6e outsb %ds:(%rsi),(%dx)
> 38: 0f a2 cpuid
>
> which confuses objtool. Presumably that would confuse other users of
> the decoder as well.
Good catch! It should be problematic, since x86 decoder sanity test is
based on objtool. But I don't want to change the test code itself,
because this problem is highly depending on Xen.
> That's a highly unlikely sequence of instructions, maybe the kernel
> decoder should recognize it as a single instruction.
OK, it is better to be done in decoder (only for CONFIG_XEN_PVHVM)
BTW, could you also share what test case would you using?
And what about attached patch? (just compile checked with/without CONFIG_XEN_PVHVM)
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
[-- Attachment #2: 0001-x86-xen-insn-Decode-XEN_EMULATE_PREFIX-correctly.patch --]
[-- Type: text/x-diff, Size: 3404 bytes --]
From 9a46833c54fd320afd3836c0e51ade82e4bc6f96 Mon Sep 17 00:00:00 2001
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Thu, 29 Aug 2019 10:01:55 +0900
Subject: [PATCH] x86: xen: insn: Decode XEN_EMULATE_PREFIX correctly
Add XEN_EMULATE_PREFIX prefix support to x86 insn decoder.
This treats a special sequence of instructions of XEN_EMULATE_PREFIX
as a prefix bytes in x86 insn decoder only if CONFIG_XEN_PVHVM=y.
Note that this prefix is treated as just a dummy code.
Reported-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
arch/x86/include/asm/xen/interface.h | 8 +++++--
arch/x86/lib/insn.c | 35 ++++++++++++++++++++++++++++
2 files changed, 41 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/xen/interface.h b/arch/x86/include/asm/xen/interface.h
index 62ca03ef5c65..fbee520b1f07 100644
--- a/arch/x86/include/asm/xen/interface.h
+++ b/arch/x86/include/asm/xen/interface.h
@@ -27,6 +27,8 @@
#ifndef _ASM_X86_XEN_INTERFACE_H
#define _ASM_X86_XEN_INTERFACE_H
+#include <linux/stringify.h>
+
/*
* XEN_GUEST_HANDLE represents a guest pointer, when passed as a field
* in a struct in memory.
@@ -379,11 +381,13 @@ struct xen_pmu_arch {
* Prefix forces emulation of some non-trapping instructions.
* Currently only CPUID.
*/
+#define __XEN_EMULATE_PREFIX 0x0f,0x0b,0x78,0x65,0x6e
+#define __XEN_EMULATE_PREFIX_STR __stringify(__XEN_EMULATE_PREFIX)
#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
diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 0b5862ba6a75..2401a6fc9509 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -7,6 +7,9 @@
#ifdef __KERNEL__
#include <linux/string.h>
+#include <linux/kernel.h>
+/* For special Xen prefix */
+#include <asm/xen/interface.h>
#else
#include <string.h>
#endif
@@ -58,6 +61,34 @@ void insn_init(struct insn *insn, const void *kaddr, int buf_len, int x86_64)
insn->addr_bytes = 4;
}
+#ifdef CONFIG_XEN_PVHVM
+static const insn_byte_t xen_prefix[] = { XEN_EMULATE_PREFIX };
+
+static int insn_xen_prefix(struct insn *insn, insn_byte_t b)
+{
+ struct insn_field *prefixes = &insn->prefixes;
+ int i = 0;
+
+ while (i < ARRAY_SIZE(xen_prefix) && b == xen_prefix[i])
+ b = peek_nbyte_next(insn_byte_t, insn, ++i);
+
+ if (unlikely(i == ARRAY_SIZE(xen_prefix))) {
+ memcpy(prefixes->bytes, xen_prefix, 3);
+ prefixes->bytes[3] = xen_prefix[ARRAY_SIZE(xen_prefix) - 1];
+ prefixes->nbytes = ARRAY_SIZE(xen_prefix);
+ insn->next_byte += prefixes->nbytes;
+ prefixes->got = 1;
+
+ return 1;
+ }
+
+err_out:
+ return 0;
+}
+#else
+#define insn_xen_prefix(insn,b) (0)
+#endif
+
/**
* insn_get_prefixes - scan x86 instruction prefix bytes
* @insn: &struct insn containing instruction
@@ -79,6 +110,10 @@ void insn_get_prefixes(struct insn *insn)
nb = 0;
lb = 0;
b = peek_next(insn_byte_t, insn);
+
+ if (insn_xen_prefix(insn, b))
+ return;
+
attr = inat_get_opcode_attribute(b);
while (inat_is_legacy_prefix(attr)) {
/* Skip if same prefix */
--
2.20.1
next prev parent reply other threads:[~2019-08-29 1:54 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-27 9:05 linux-next: Tree for Aug 27 Stephen Rothwell
2019-08-27 15:18 ` linux-next: Tree for Aug 27 (amdgpu) Randy Dunlap
2019-08-27 15:41 ` Alex Deucher
2019-08-27 15:24 ` linux-next: Tree for Aug 27 (mshyperv.c) Randy Dunlap
2019-08-27 15:29 ` linux-next: Tree for Aug 27 (kunit) Randy Dunlap
2019-08-27 16:09 ` Brendan Higgins
2019-08-27 16:12 ` shuah
2019-08-27 15:37 ` linux-next: Tree for Aug 27 (mm/zsmalloc.c) Randy Dunlap
2019-08-28 5:30 ` Sergey Senozhatsky
2019-08-27 15:40 ` linux-next: Tree for Aug 27 (objtool) Randy Dunlap
2019-08-27 15:59 ` Josh Poimboeuf
2019-08-27 19:05 ` Randy Dunlap
2019-08-28 15:51 ` Josh Poimboeuf
2019-08-28 16:05 ` Randy Dunlap
2019-08-28 16:13 ` Josh Poimboeuf
2019-08-28 16:34 ` Josh Poimboeuf
2019-08-29 1:53 ` Masami Hiramatsu [this message]
2019-08-29 17:59 ` Josh Poimboeuf
2019-08-30 6:23 ` Masami Hiramatsu
2019-08-30 15:14 ` Masami Hiramatsu
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