Re: [PATCH 1/5] x86: Implement __WARN using UD0
From: Peter Zijlstra
Date: Wed Mar 22 2017 - 04:47:26 EST
A little like so then.
---
Subject: x86: Implement __WARN using UD0
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu Feb 2 14:43:51 CET 2017
By using "UD0" for WARNs we remove the function call and its possible
__FILE__ and __LINE__ immediate arguments from the instruction stream.
Total image size will not change much, what we win in the instruction
stream we'll loose because of the __bug_table entries. Still, saves on
I$ footprint and the total image size does go down a bit.
text data bss dec hex filename
10702123 4530992 843776 16076891 f5505b defconfig-build/vmlinux.0
10682460 4530992 843776 16057228 f5038c defconfig-build/vmlinux.1
(um didn't seem to use GENERIC_BUG at all, so remove it)
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Richard Weinberger <richard.weinberger@xxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/um/Kconfig.common | 5 --
arch/x86/include/asm/bug.h | 73 +++++++++++++++++++++++++++++++----------
arch/x86/kernel/dumpstack.c | 3 -
arch/x86/kernel/dumpstack_32.c | 12 ------
arch/x86/kernel/dumpstack_64.c | 10 -----
arch/x86/kernel/traps.c | 46 ++++++++++++++++++++++---
arch/x86/um/Makefile | 2 -
arch/x86/um/bug.c | 21 -----------
8 files changed, 97 insertions(+), 75 deletions(-)
--- a/arch/um/Kconfig.common
+++ b/arch/um/Kconfig.common
@@ -50,11 +50,6 @@ config GENERIC_CALIBRATE_DELAY
bool
default y
-config GENERIC_BUG
- bool
- default y
- depends on BUG
-
config HZ
int
default 100
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -1,36 +1,75 @@
#ifndef _ASM_X86_BUG_H
#define _ASM_X86_BUG_H
+#include <linux/stringify.h>
+
#define HAVE_ARCH_BUG
-#ifdef CONFIG_DEBUG_BUGVERBOSE
+/*
+ * Since some emulators terminate on UD2, we cannot use it for WARN.
+ * Since various instruction decoders disagree on the length of UD1,
+ * we cannot use it either. So use UD0 for WARN.
+ *
+ * (binutils knows about "ud1" but {en,de}codes it as 2 bytes, whereas
+ * our kernel decoder thinks it takes a ModRM byte, which seems consistent
+ * with various things like the Intel SDM instruction encoding rules)
+ */
+
+#define ASM_UD0 ".byte 0x0f, 0xff"
+#define ASM_UD1 ".byte 0x0f, 0xb9" /* + ModRM */
+#define ASM_UD2 ".byte 0x0f, 0x0b"
+
+#define INSN_UD0 0xff0f
+#define INSN_UD2 0x0b0f
+
+#define LEN_UD0 2
#ifdef CONFIG_X86_32
-# define __BUG_C0 "2:\t.long 1b, %c0\n"
+# define __BUG_REL(val) ".long " __stringify(val)
#else
-# define __BUG_C0 "2:\t.long 1b - 2b, %c0 - 2b\n"
+# define __BUG_REL(val) ".long " __stringify(val) " - 2b"
#endif
-#define BUG() \
-do { \
- asm volatile("1:\tud2\n" \
- ".pushsection __bug_table,\"a\"\n" \
- __BUG_C0 \
- "\t.word %c1, 0\n" \
- "\t.org 2b+%c2\n" \
- ".popsection" \
- : : "i" (__FILE__), "i" (__LINE__), \
- "i" (sizeof(struct bug_entry))); \
- unreachable(); \
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+
+#define _BUG_FLAGS(ins, flags) \
+do { \
+ asm volatile("1:\t" ins "\n" \
+ ".pushsection __bug_table,\"a\"\n" \
+ "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
+ "\t" __BUG_REL(%c0) "\t# bug_entry::file\n" \
+ "\t.word %c1" "\t# bug_entry::line\n" \
+ "\t.word %c2" "\t# bug_entry::flags\n" \
+ "\t.org 2b+%c3\n" \
+ ".popsection" \
+ : : "i" (__FILE__), "i" (__LINE__), \
+ "i" (flags), \
+ "i" (sizeof(struct bug_entry))); \
} while (0)
-#else
+#else /* !CONFIG_DEBUG_BUGVERBOSE */
+
+#define _BUG_FLAGS(ins, flags) \
+do { \
+ asm volatile("1:\t" ins "\n" \
+ ".pushsection __bug_table,\"a\"\n" \
+ "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
+ "\t.word %c0" "\t# bug_entry::flags\n" \
+ "\t.org 2b+%c1\n" \
+ ".popsection" \
+ : : "i" (flags), \
+ "i" (sizeof(struct bug_entry))); \
+} while (0)
+
+#endif /* CONFIG_DEBUG_BUGVERBOSE */
+
#define BUG() \
do { \
- asm volatile("ud2"); \
+ _BUG_FLAGS(ASM_UD2, 0); \
unreachable(); \
} while (0)
-#endif
+
+#define __WARN_TAINT(taint) _BUG_FLAGS(ASM_UD0, BUGFLAG_TAINT(taint))
#include <asm-generic/bug.h>
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -289,9 +289,6 @@ void die(const char *str, struct pt_regs
unsigned long flags = oops_begin();
int sig = SIGSEGV;
- if (!user_mode(regs))
- report_bug(regs->ip, regs);
-
if (__die(str, regs, err))
sig = 0;
oops_end(flags, regs, sig);
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -162,15 +162,3 @@ void show_regs(struct pt_regs *regs)
}
pr_cont("\n");
}
-
-int is_valid_bugaddr(unsigned long ip)
-{
- unsigned short ud2;
-
- if (ip < PAGE_OFFSET)
- return 0;
- if (probe_kernel_address((unsigned short *)ip, ud2))
- return 0;
-
- return ud2 == 0x0b0f;
-}
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -178,13 +178,3 @@ void show_regs(struct pt_regs *regs)
}
pr_cont("\n");
}
-
-int is_valid_bugaddr(unsigned long ip)
-{
- unsigned short ud2;
-
- if (__copy_from_user(&ud2, (const void __user *) ip, sizeof(ud2)))
- return 0;
-
- return ud2 == 0x0b0f;
-}
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -169,6 +169,37 @@ void ist_end_non_atomic(void)
preempt_disable();
}
+int is_valid_bugaddr(unsigned long addr)
+{
+ unsigned short ud;
+
+ if (addr < TASK_SIZE_MAX)
+ return 0;
+
+ if (probe_kernel_address((unsigned short *)addr, ud))
+ return 0;
+
+ return ud == INSN_UD0 || ud == INSN_UD2;
+}
+
+static int fixup_bug(struct pt_regs *regs, int trapnr)
+{
+ if (trapnr != X86_TRAP_UD)
+ return 0;
+
+ switch (report_bug(regs->ip, regs)) {
+ case BUG_TRAP_TYPE_NONE:
+ case BUG_TRAP_TYPE_BUG:
+ break;
+
+ case BUG_TRAP_TYPE_WARN:
+ regs->ip += LEN_UD0;
+ return 1;
+ }
+
+ return 0;
+}
+
static nokprobe_inline int
do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
struct pt_regs *regs, long error_code)
@@ -187,12 +218,15 @@ do_trap_no_signal(struct task_struct *ts
}
if (!user_mode(regs)) {
- if (!fixup_exception(regs, trapnr)) {
- tsk->thread.error_code = error_code;
- tsk->thread.trap_nr = trapnr;
- die(str, regs, error_code);
- }
- return 0;
+ if (fixup_exception(regs, trapnr))
+ return 0;
+
+ if (fixup_bug(regs, trapnr))
+ return 0;
+
+ tsk->thread.error_code = error_code;
+ tsk->thread.trap_nr = trapnr;
+ die(str, regs, error_code);
}
return -1;
--- a/arch/x86/um/Makefile
+++ b/arch/x86/um/Makefile
@@ -8,7 +8,7 @@ else
BITS := 64
endif
-obj-y = bug.o bugs_$(BITS).o delay.o fault.o ldt.o \
+obj-y = bugs_$(BITS).o delay.o fault.o ldt.o \
ptrace_$(BITS).o ptrace_user.o setjmp_$(BITS).o signal.o \
stub_$(BITS).o stub_segv.o \
sys_call_table_$(BITS).o sysrq_$(BITS).o tls_$(BITS).o \
--- a/arch/x86/um/bug.c
+++ /dev/null
@@ -1,21 +0,0 @@
-/*
- * Copyright (C) 2006 Jeff Dike (jdike@xxxxxxxxxxx)
- * Licensed under the GPL V2
- */
-
-#include <linux/uaccess.h>
-
-/*
- * Mostly copied from i386/x86_86 - eliminated the eip < PAGE_OFFSET because
- * that's not relevant in skas mode.
- */
-
-int is_valid_bugaddr(unsigned long eip)
-{
- unsigned short ud2;
-
- if (probe_kernel_address((unsigned short __user *)eip, ud2))
- return 0;
-
- return ud2 == 0x0b0f;
-}