Messages in this thread | | | Date | Thu, 18 Nov 2021 20:55:04 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH V5 03/50] x86/traps: Remove stack-protector from traps.c |
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On Wed, Nov 10, 2021 at 07:56:49PM +0800, Lai Jiangshan wrote: > From: Lai Jiangshan <laijs@linux.alibaba.com> > > When stack-protector is enabled, the compiler adds some instrument code > at the beginning and the end of some functions. Many functions in traps.c > are non-instrumentable. Moreover, stack-protector code in the beginning > of the affected function accesses the canary that might be watched by > hardware breakpoints which also violate the non-instrumentable > nature of some functions and might cause infinite recursive #DB because > the canary is accessed before resetting the dr7. > > So it is better to remove stack-protector from traps.c. > > It is also prepared for later patches that move some entry code into > traps.c, some of which can NOT use percpu register until gsbase is > properly switched. And stack-protector depends on the percpu register > to work. > > Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com> > --- > arch/x86/kernel/Makefile | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > index 2ff3e600f426..8ac45801ba8b 100644 > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -50,6 +50,7 @@ KCOV_INSTRUMENT := n > > CFLAGS_head$(BITS).o += -fno-stack-protector > CFLAGS_cc_platform.o += -fno-stack-protector > +CFLAGS_traps.o += -fno-stack-protector
Well, there's a lot more noinstr than just in traps. There's also real C code in traps. This isn't really a solution.
I think GCC has recently grown __attribute__((no_stack_protector)), which should be added to noinstr (GCC-11 and above).
Additionally we could add code to objtool to detect this problem.
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