Messages in this thread Patch in this message | | | Date | Thu, 12 Mar 2020 14:41:07 +0100 | From | Peter Zijlstra <> | Subject | [RFC][PATCH 00/16] objtool: vmlinux.o and noinstr validation |
| |
Hi all,
These patches extend objtool to be able to run on vmlinux.o and validate Thomas's proposed noinstr annotation:
https://lkml.kernel.org/r/20200310170951.87c29e9c1cfbddd93ccd92b3@kernel.org
"That's why we want the sections and the annotation. If something calls out of a noinstr section into a regular text section and the call is not annotated at the call site, then objtool can complain and tell you. What Peter and I came up with looks like this:
noinstr foo() do_protected(); <- Safe because in the noinstr section instr_begin(); <- Marks the begin of a safe region, ignored by objtool do_stuff(); <- All good instr_end(); <- End of the safe region. objtool starts looking again do_other_stuff(); <- Unsafe because do_other_stuff() is not protected
and:
noinstr do_protected() bar(); <- objtool will complain here "
It should be accompanied by something like the below; which you'll find in a series by Thomas.
---
--- a/include/asm-generic/sections.h +++ b/include/asm-generic/sections.h @@ -53,6 +53,9 @@ extern char __ctors_start[], __ctors_end /* Start and end of .opd section - used for function descriptors. */ extern char __start_opd[], __end_opd[]; +/* Start and end of instrumentation protected text section */ +extern char __noinstr_text_start[], __noinstr_text_end[]; + extern __visible const void __nosave_begin, __nosave_end; /* Function descriptor handling (if any). Override in asm/sections.h */ --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -550,6 +550,10 @@ #define TEXT_TEXT \ ALIGN_FUNCTION(); \ *(.text.hot TEXT_MAIN .text.fixup .text.unlikely) \ + ALIGN_FUNCTION(); \ + __noinstr_text_start = .; \ + *(.noinstr.text) \ + __noinstr_text_end = .; \ *(.text..refcount) \ *(.ref.text) \ MEM_KEEP(init.text*) \ --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -120,12 +120,37 @@ void ftrace_likely_update(struct ftrace_ /* Annotate a C jump table to allow objtool to follow the code flow */ #define __annotate_jump_table __section(.rodata..c_jump_table) +/* Begin/end of an instrumentation safe region */ +#define instr_begin() ({ \ + asm volatile("%c0:\n\t" \ + ".pushsection .discard.instr_begin\n\t" \ + ".long %c0b - .\n\t" \ + ".popsection\n\t" : : "i" (__COUNTER__)); \ +}) + +#define instr_end() ({ \ + asm volatile("%c0:\n\t" \ + ".pushsection .discard.instr_end\n\t" \ + ".long %c0b - .\n\t" \ + ".popsection\n\t" : : "i" (__COUNTER__)); \ +}) + #else #define annotate_reachable() #define annotate_unreachable() #define __annotate_jump_table +#define instr_begin() do { } while(0) +#define instr_end() do { } while(0) #endif +#define INSTR(expr) ({ \ + typeof(({ expr; })) __ret; \ + instr_begin(); \ + __ret = ({ expr; }); \ + instr_end(); \ + __ret; \ +}) + #ifndef ASM_UNREACHABLE # define ASM_UNREACHABLE #endif --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -118,6 +118,11 @@ struct ftrace_likely_data { #define notrace __attribute__((__no_instrument_function__)) #endif +/* Section for code which can't be instrumented at all */ +#define noinstr \ + notrace __attribute((__section__(".noinstr.text"))) + + /* * it doesn't make sense on ARM (currently the only user of __naked) * to trace naked functions because then mcount is called without --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -953,7 +953,7 @@ static void check_section(const char *mo #define DATA_SECTIONS ".data", ".data.rel" #define TEXT_SECTIONS ".text", ".text.unlikely", ".sched.text", \ - ".kprobes.text", ".cpuidle.text" + ".kprobes.text", ".cpuidle.text", ".noinstr.text" #define OTHER_TEXT_SECTIONS ".ref.text", ".head.text", ".spinlock.text", \ ".fixup", ".entry.text", ".exception.text", ".text.*", \ ".coldtext"
| |