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@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
This implies that the backport is incorrect, so I'll wait for an updated version...
thanks,
greg k-h