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Date: Thu, 14 May 2020 14:20:38 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Marco Elver <elver@...gle.com>
Cc: Will Deacon <will@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
"Paul E. McKenney" <paulmck@...nel.org>,
Ingo Molnar <mingo@...nel.org>,
Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen
On Thu, May 14, 2020 at 01:21:42PM +0200, Peter Zijlstra wrote:
> Given the patch below (on top of tglx's entry-v5-the-rest tag); I did
> find that I could actually build alternative.o for gcc-{8,9,10} and
> indeed clang-10. Any earlier gcc (I tried, 5,6,7) does not build:
Damn!, I forgot the patch from https://lkml.kernel.org/r/20200513111447.GE3001@hirez.programming.kicks-ass.net
With that included, on a GCC-10 KCSAN+UBSAN build, I now get this, and
that is very much not okay. This is the thing Will complained about as
well I think.
Hohumm :-(
---
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index d6d61c4455fa..ba89cabe5fcf 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -28,10 +28,6 @@ KASAN_SANITIZE_dumpstack_$(BITS).o := n
KASAN_SANITIZE_stacktrace.o := n
KASAN_SANITIZE_paravirt.o := n
-# With some compiler versions the generated code results in boot hangs, caused
-# by several compilation units. To be safe, disable all instrumentation.
-KCSAN_SANITIZE := n
-
OBJECT_FILES_NON_STANDARD_test_nx.o := y
OBJECT_FILES_NON_STANDARD_paravirt_patch.o := y
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 77c83833d91e..06d8db612efc 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -990,7 +990,7 @@ static __always_inline int patch_cmp(const void *key, const void *elt)
return 0;
}
-int noinstr poke_int3_handler(struct pt_regs *regs)
+int noinstr __no_kcsan __no_sanitize_address __no_sanitize_undefined poke_int3_handler(struct pt_regs *regs)
{
struct bp_patching_desc *desc;
struct text_poke_loc *tp;
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 2cb42d8bdedc..c728ae9dcf96 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -15,6 +15,9 @@
/* all clang versions usable with the kernel support KASAN ABI version 5 */
#define KASAN_ABI_VERSION 5
+#define __no_sanitize_undefined \
+ __attribute__((no_sanitize("undefined")))
+
#if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer)
/* Emulate GCC's __SANITIZE_ADDRESS__ flag */
#define __SANITIZE_ADDRESS__
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 7dd4e0349ef3..8196a121a78e 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -138,6 +138,12 @@
#define KASAN_ABI_VERSION 3
#endif
+#if __has_attribute(__no_sanitize_undefined__)
+#define __no_sanitize_undefined __attribute__((no_sanitize_undefined))
+#else
+#define __no_sanitize_undefined
+#endif
+
#if __has_attribute(__no_sanitize_address__)
#define __no_sanitize_address __attribute__((no_sanitize_address))
#else
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 3bb962959d8b..2ea532b19e75 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -241,12 +241,12 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
* atomicity or dependency ordering guarantees. Note that this may result
* in tears!
*/
-#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x))
+#define __READ_ONCE(x) data_race((*(const volatile __unqual_scalar_typeof(x) *)&(x)))
#define __READ_ONCE_SCALAR(x) \
({ \
typeof(x) *__xp = &(x); \
- __unqual_scalar_typeof(x) __x = data_race(__READ_ONCE(*__xp)); \
+ __unqual_scalar_typeof(x) __x = __READ_ONCE(*__xp); \
kcsan_check_atomic_read(__xp, sizeof(*__xp)); \
smp_read_barrier_depends(); \
(typeof(x))__x; \
@@ -260,14 +260,14 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
#define __WRITE_ONCE(x, val) \
do { \
- *(volatile typeof(x) *)&(x) = (val); \
+ data_race(*(volatile typeof(x) *)&(x) = (val)); \
} while (0)
#define __WRITE_ONCE_SCALAR(x, val) \
do { \
typeof(x) *__xp = &(x); \
kcsan_check_atomic_write(__xp, sizeof(*__xp)); \
- data_race(({ __WRITE_ONCE(*__xp, val); 0; })); \
+ __WRITE_ONCE(*__xp, val); \
} while (0)
#define WRITE_ONCE(x, val) \
---
0000 0000000000000000 <poke_int3_handler>:
0000 0: 41 55 push %r13
0002 2: 41 54 push %r12
0004 4: 55 push %rbp
0005 5: 53 push %rbx
0006 6: 48 83 ec 10 sub $0x10,%rsp
000a a: 65 48 8b 04 25 28 00 mov %gs:0x28,%rax
0011 11: 00 00
0013 13: 48 89 44 24 08 mov %rax,0x8(%rsp)
0018 18: 31 c0 xor %eax,%eax
001a 1a: f6 87 88 00 00 00 03 testb $0x3,0x88(%rdi)
0021 21: 74 21 je 44 <poke_int3_handler+0x44>
0023 23: 31 c0 xor %eax,%eax
0025 25: 48 8b 4c 24 08 mov 0x8(%rsp),%rcx
002a 2a: 65 48 2b 0c 25 28 00 sub %gs:0x28,%rcx
0031 31: 00 00
0033 33: 0f 85 79 01 00 00 jne 1b2 <poke_int3_handler+0x1b2>
0039 39: 48 83 c4 10 add $0x10,%rsp
003d 3d: 5b pop %rbx
003e 3e: 5d pop %rbp
003f 3f: 41 5c pop %r12
0041 41: 41 5d pop %r13
0043 43: c3 retq
0044 44: 48 89 fb mov %rdi,%rbx
0047 47: e8 00 00 00 00 callq 4c <poke_int3_handler+0x4c>
0048 48: R_X86_64_PLT32 kcsan_disable_current-0x4
004c 4c: 4c 8b 2d 00 00 00 00 mov 0x0(%rip),%r13 # 53 <poke_int3_handler+0x53>
004f 4f: R_X86_64_PC32 .bss+0x101c
0053 53: 48 8d 6c 24 08 lea 0x8(%rsp),%rbp
0058 58: 49 89 e4 mov %rsp,%r12
005b 5b: 48 89 e8 mov %rbp,%rax
005e 5e: 4c 29 e0 sub %r12,%rax
0061 61: 48 83 f8 08 cmp $0x8,%rax
0065 65: 0f 87 4c 01 00 00 ja 1b7 <poke_int3_handler+0x1b7>
006b 6b: 4c 29 e5 sub %r12,%rbp
006e 6e: 4c 89 2c 24 mov %r13,(%rsp)
0072 72: e8 00 00 00 00 callq 77 <poke_int3_handler+0x77>
0073 73: R_X86_64_PLT32 kcsan_enable_current_nowarn-0x4
0077 77: 48 83 fd 08 cmp $0x8,%rbp
007b 7b: 0f 87 53 01 00 00 ja 1d4 <poke_int3_handler+0x1d4>
0081 81: 4c 8b 24 24 mov (%rsp),%r12
0085 85: 4d 85 e4 test %r12,%r12
0088 88: 74 99 je 23 <poke_int3_handler+0x23>
008a 8a: e8 00 00 00 00 callq 8f <poke_int3_handler+0x8f>
008b 8b: R_X86_64_PLT32 kcsan_disable_current-0x4
008f 8f: 4d 8d 6c 24 0c lea 0xc(%r12),%r13
0094 94: 41 8b 6c 24 0c mov 0xc(%r12),%ebp
0099 99: e8 00 00 00 00 callq 9e <poke_int3_handler+0x9e>
009a 9a: R_X86_64_PLT32 kcsan_enable_current_nowarn-0x4
009e 9e: 85 ed test %ebp,%ebp
00a0 a0: 74 81 je 23 <poke_int3_handler+0x23>
00a2 a2: 8d 55 01 lea 0x1(%rbp),%edx
00a5 a5: 89 e8 mov %ebp,%eax
00a7 a7: f0 41 0f b1 55 00 lock cmpxchg %edx,0x0(%r13)
00ad ad: 89 c5 mov %eax,%ebp
00af af: 75 ed jne 9e <poke_int3_handler+0x9e>
00b1 b1: 48 8b bb 80 00 00 00 mov 0x80(%rbx),%rdi
00b8 b8: 49 63 44 24 08 movslq 0x8(%r12),%rax
00bd bd: 49 8b 0c 24 mov (%r12),%rcx
00c1 c1: 48 8d 57 ff lea -0x1(%rdi),%rdx
00c5 c5: 83 f8 01 cmp $0x1,%eax
00c8 c8: 7f 1c jg e6 <poke_int3_handler+0xe6>
00ca ca: 48 63 31 movslq (%rcx),%rsi
00cd cd: 31 c0 xor %eax,%eax
00cf cf: 48 81 c6 00 00 00 00 add $0x0,%rsi
00d2 d2: R_X86_64_32S _stext
00d6 d6: 48 39 f2 cmp %rsi,%rdx
00d9 d9: 74 3c je 117 <poke_int3_handler+0x117>
00db db: f0 41 ff 4c 24 0c lock decl 0xc(%r12)
00e1 e1: e9 3f ff ff ff jmpq 25 <poke_int3_handler+0x25>
00e6 e6: 49 89 c9 mov %rcx,%r9
00e9 e9: 49 89 c0 mov %rax,%r8
00ec ec: 49 d1 e8 shr %r8
00ef ef: 4c 89 c1 mov %r8,%rcx
00f2 f2: 48 c1 e1 04 shl $0x4,%rcx
00f6 f6: 4c 01 c9 add %r9,%rcx
00f9 f9: 48 63 31 movslq (%rcx),%rsi
00fc fc: 48 81 c6 00 00 00 00 add $0x0,%rsi
00ff ff: R_X86_64_32S _stext
0103 103: 48 39 f2 cmp %rsi,%rdx
0106 106: 0f 82 88 00 00 00 jb 194 <poke_int3_handler+0x194>
010c 10c: 0f 87 93 00 00 00 ja 1a5 <poke_int3_handler+0x1a5>
0112 112: 48 85 c9 test %rcx,%rcx
0115 115: 74 28 je 13f <poke_int3_handler+0x13f>
0117 117: 0f b6 41 08 movzbl 0x8(%rcx),%eax
011b 11b: 8d 70 34 lea 0x34(%rax),%esi
011e 11e: 40 80 fe 1f cmp $0x1f,%sil
0122 122: 76 02 jbe 126 <poke_int3_handler+0x126>
0124 124: 0f 0b ud2
0126 126: 40 0f b6 f6 movzbl %sil,%esi
012a 12a: 48 0f be b6 00 00 00 movsbq 0x0(%rsi),%rsi
0131 131: 00
012e 12e: R_X86_64_32S .rodata
0132 132: 48 01 f2 add %rsi,%rdx
0135 135: 3c e8 cmp $0xe8,%al
0137 137: 74 29 je 162 <poke_int3_handler+0x162>
0139 139: 77 08 ja 143 <poke_int3_handler+0x143>
013b 13b: 3c cc cmp $0xcc,%al
013d 13d: 75 e5 jne 124 <poke_int3_handler+0x124>
013f 13f: 31 c0 xor %eax,%eax
0141 141: eb 98 jmp db <poke_int3_handler+0xdb>
0143 143: 83 e0 fd and $0xfffffffd,%eax
0146 146: 3c e9 cmp $0xe9,%al
0148 148: 75 da jne 124 <poke_int3_handler+0x124>
014a 14a: 48 63 41 04 movslq 0x4(%rcx),%rax
014e 14e: 48 01 c2 add %rax,%rdx
0151 151: b8 01 00 00 00 mov $0x1,%eax
0156 156: 48 89 93 80 00 00 00 mov %rdx,0x80(%rbx)
015d 15d: e9 79 ff ff ff jmpq db <poke_int3_handler+0xdb>
0162 162: 48 63 41 04 movslq 0x4(%rcx),%rax
0166 166: 48 83 c7 04 add $0x4,%rdi
016a 16a: 48 01 c2 add %rax,%rdx
016d 16d: 48 8b 83 98 00 00 00 mov 0x98(%rbx),%rax
0174 174: 48 8d 48 f8 lea -0x8(%rax),%rcx
0178 178: 48 89 8b 98 00 00 00 mov %rcx,0x98(%rbx)
017f 17f: 48 89 78 f8 mov %rdi,-0x8(%rax)
0183 183: b8 01 00 00 00 mov $0x1,%eax
0188 188: 48 89 93 80 00 00 00 mov %rdx,0x80(%rbx)
018f 18f: e9 47 ff ff ff jmpq db <poke_int3_handler+0xdb>
0194 194: 4c 89 c0 mov %r8,%rax
0197 197: 48 85 c0 test %rax,%rax
019a 19a: 0f 85 49 ff ff ff jne e9 <poke_int3_handler+0xe9>
01a0 1a0: e9 36 ff ff ff jmpq db <poke_int3_handler+0xdb>
01a5 1a5: 48 83 e8 01 sub $0x1,%rax
01a9 1a9: 4c 8d 49 10 lea 0x10(%rcx),%r9
01ad 1ad: 48 d1 e8 shr %rax
01b0 1b0: eb e5 jmp 197 <poke_int3_handler+0x197>
01b2 1b2: e8 00 00 00 00 callq 1b7 <poke_int3_handler+0x1b7>
01b3 1b3: R_X86_64_PLT32 __stack_chk_fail-0x4
01b7 1b7: 4c 01 e0 add %r12,%rax
01ba 1ba: 0f 82 ab fe ff ff jb 6b <poke_int3_handler+0x6b>
01c0 1c0: 4c 89 e6 mov %r12,%rsi
01c3 1c3: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
01c6 1c6: R_X86_64_32S .data+0x80
01ca 1ca: e8 00 00 00 00 callq 1cf <poke_int3_handler+0x1cf>
01cb 1cb: R_X86_64_PLT32 __ubsan_handle_type_mismatch_v1-0x4
01cf 1cf: e9 97 fe ff ff jmpq 6b <poke_int3_handler+0x6b>
01d4 1d4: 4c 01 e5 add %r12,%rbp
01d7 1d7: 0f 82 a4 fe ff ff jb 81 <poke_int3_handler+0x81>
01dd 1dd: 4c 89 e6 mov %r12,%rsi
01e0 1e0: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
01e3 1e3: R_X86_64_32S .data+0x60
01e7 1e7: e8 00 00 00 00 callq 1ec <poke_int3_handler+0x1ec>
01e8 1e8: R_X86_64_PLT32 __ubsan_handle_type_mismatch_v1-0x4
01ec 1ec: e9 90 fe ff ff jmpq 81 <poke_int3_handler+0x81>
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