Messages in this thread | | | Subject | Re: [for-stable-4.19 PATCH 1/2] vmlinux.lds.h: Create section for protection against instrumentation | From | Alexandre Chartre <> | Date | Fri, 19 Mar 2021 12:20:22 +0100 |
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On 3/19/21 11:39 AM, Greg Kroah-Hartman wrote: > On Fri, Mar 19, 2021 at 07:54:15AM +0800, Nicolas Boichat wrote: >> From: Thomas Gleixner <tglx@linutronix.de> >> >> commit 6553896666433e7efec589838b400a2a652b3ffa upstream. >> >> Some code pathes, especially the low level entry code, must be protected >> against instrumentation for various reasons: >> >> - Low level entry code can be a fragile beast, especially on x86. >> >> - With NO_HZ_FULL RCU state needs to be established before using it. >> >> Having a dedicated section for such code allows to validate with tooling >> that no unsafe functions are invoked. >> >> Add the .noinstr.text section and the noinstr attribute to mark >> functions. noinstr implies notrace. Kprobes will gain a section check >> later. >> >> Provide also a set of markers: instrumentation_begin()/end() >> >> These are used to mark code inside a noinstr function which calls >> into regular instrumentable text section as safe. >> >> The instrumentation markers are only active when CONFIG_DEBUG_ENTRY is >> enabled as the end marker emits a NOP to prevent the compiler from merging >> the annotation points. This means the objtool verification requires a >> kernel compiled with this option. >> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> >> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com> >> Acked-by: Peter Zijlstra <peterz@infradead.org> >> Link: https://lkml.kernel.org/r/20200505134100.075416272@linutronix.de >> >> [Nicolas: context conflicts in: >> arch/powerpc/kernel/vmlinux.lds.S >> include/asm-generic/vmlinux.lds.h >> include/linux/compiler.h >> include/linux/compiler_types.h] >> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org> > > Did you build this on x86? > > I get the following build error: > > ld:./arch/x86/kernel/vmlinux.lds:20: syntax error > > And that line looks like: > > . = ALIGN(8); *(.text.hot .text.hot.*) *(.text .text.fixup) *(.text.unlikely .text.unlikely.*) *(.text.unknown .text.unknown.*) . = ALIGN(8); __noinstr_text_start = .; *(.__attribute__((noinline)) __attribute__((no_instrument_function)) __attribute((__section__(".noinstr.text"))).text) __noinstr_text_end = .; *(.text..refcount) *(.ref.text) *(.meminit.text*) *(.memexit.text*) >
In the NOINSTR_TEXT macro, noinstr is expanded with the value of the noinstr macro from linux/compiler_types.h while it shouldn't.
The problem is possibly that the noinstr macro is defined for assembly. Make sure that the macro is not defined for assembly e.g.:
#ifndef __ASSEMBLY__
/* Section for code which can't be instrumented at all */ #define noinstr \ noinline notrace __attribute((__section__(".noinstr.text")))
#endif
alex.
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