From d7c65f1f9bb5144b9ea45ab52acb3e3e1fc94207 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Mon, 22 Mar 2021 10:35:13 +0800 Subject: [PATCH 2632/2944] compiler.h: Move instrumentation_begin()/end() to new header to #30648216 commit d19e789f068b3d633cbac430764962f404198022 upstream. Linus pointed out that compiler.h - which is a key header that gets included in every single one of the 28,000+ kernel files during a kernel build - was bloated in: 655389666643: ("vmlinux.lds.h: Create section for protection against instrumentation") Linus noted: > I have pulled this, but do we really want to add this to a header file > that is _so_ core that it gets included for basically every single > file built? > > I don't even see those instrumentation_begin/end() things used > anywhere right now. > > It seems excessive. That 53 lines is maybe not a lot, but it pushed > that header file to over 12kB, and while it's mostly comments, it's > extra IO and parsing basically for _every_ single file compiled in the > kernel. > > For what appears to be absolutely zero upside right now, and I really > don't see why this should be in such a core header file! Move these primitives into a new header: , and include that header in the headers that make use of it. Unfortunately one of these headers is asm-generic/bug.h, which does get included in a lot of places, similarly to compiler.h. So the de-bloating effect isn't as good as we'd like it to be - but at least the interfaces are defined separately. No change to functionality intended. Reported-by: Linus Torvalds Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20200604071921.GA1361070@gmail.com Cc: Thomas Gleixner Cc: Borislav Petkov Cc: Peter Zijlstra Signed-off-by: Ethan Zhao Signed-off-by: Zelin Deng Reviewed-by: Artie Ding --- arch/x86/include/asm/bug.h | 1 + include/asm-generic/bug.h | 1 + include/linux/compiler.h | 5 ++++ include/linux/context_tracking.h | 2 ++ include/linux/instrumentation.h | 57 ++++++++++++++++++++++++++++++++++++++++ 5 files changed, 66 insertions(+) create mode 100644 include/linux/instrumentation.h diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h index 6804d66..af91e3d 100644 --- a/arch/x86/include/asm/bug.h +++ b/arch/x86/include/asm/bug.h @@ -3,6 +3,7 @@ #define _ASM_X86_BUG_H #include +#include /* * Despite that some emulators terminate on UD2, we use it for WARN(). diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h index d4fb510..0a9cc39 100644 --- a/include/asm-generic/bug.h +++ b/include/asm-generic/bug.h @@ -3,6 +3,7 @@ #define _ASM_GENERIC_BUG_H #include +#include #define CUT_HERE "------------[ cut here ]------------\n" diff --git a/include/linux/compiler.h b/include/linux/compiler.h index bb22908..3b3986e 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -115,9 +115,14 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, ".pushsection .discard.unreachable\n\t" \ ".long 999b - .\n\t" \ ".popsection\n\t" + +/* Annotate a C jump table to allow objtool to follow the code flow */ +#define __annotate_jump_table __section(.rodata..c_jump_table) + #else #define annotate_reachable() #define annotate_unreachable() +#define __annotate_jump_table #endif #ifndef ASM_UNREACHABLE diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index d05609ad3..bd4a566 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -5,6 +5,8 @@ #include #include #include +#include + #include diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h new file mode 100644 index 0000000..93e2ad6 --- /dev/null +++ b/include/linux/instrumentation.h @@ -0,0 +1,57 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __LINUX_INSTRUMENTATION_H +#define __LINUX_INSTRUMENTATION_H + +#if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_VALIDATION) + +/* Begin/end of an instrumentation safe region */ +#define instrumentation_begin() ({ \ + asm volatile("%c0: nop\n\t" \ + ".pushsection .discard.instr_begin\n\t" \ + ".long %c0b - .\n\t" \ + ".popsection\n\t" : : "i" (__COUNTER__)); \ +}) + +/* + * Because instrumentation_{begin,end}() can nest, objtool validation considers + * _begin() a +1 and _end() a -1 and computes a sum over the instructions. + * When the value is greater than 0, we consider instrumentation allowed. + * + * There is a problem with code like: + * + * noinstr void foo() + * { + * instrumentation_begin(); + * ... + * if (cond) { + * instrumentation_begin(); + * ... + * instrumentation_end(); + * } + * bar(); + * instrumentation_end(); + * } + * + * If instrumentation_end() would be an empty label, like all the other + * annotations, the inner _end(), which is at the end of a conditional block, + * would land on the instruction after the block. + * + * If we then consider the sum of the !cond path, we'll see that the call to + * bar() is with a 0-value, even though, we meant it to happen with a positive + * value. + * + * To avoid this, have _end() be a NOP instruction, this ensures it will be + * part of the condition block and does not escape. + */ +#define instrumentation_end() ({ \ + asm volatile("%c0: nop\n\t" \ + ".pushsection .discard.instr_end\n\t" \ + ".long %c0b - .\n\t" \ + ".popsection\n\t" : : "i" (__COUNTER__)); \ +}) +#else +# define instrumentation_begin() do { } while(0) +# define instrumentation_end() do { } while(0) +#endif + +#endif /* __LINUX_INSTRUMENTATION_H */ -- 1.8.3.1