On Fri, Mar 19, 2021 at 12:20:22PM +0100, Alexandre Chartre wrote: > > 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@xxxxxxxxxxxxx> > > > > > > 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@xxxxxxxxxxxxx> > > > Reviewed-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx> > > > Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > > Link: https://lkml.kernel.org/r/20200505134100.075416272@xxxxxxxxxxxxx > > > > > > [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@xxxxxxxxxxxx> > > > > 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 This implies that the backport is incorrect, so I'll wait for an updated version... thanks, greg k-h
