Re: [PATCH v3 00/11] arm64: BTI kernel and vDSO support

From: Will Deacon <will@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Amit Kachhap <amit.kachhap@arm.com>,
	Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
	Dave Martin <Dave.Martin@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 00/11] arm64: BTI kernel and vDSO support
Date: Thu, 7 May 2020 15:59:01 +0100	[thread overview]
Message-ID: <20200507145901.GA1938@willie-the-truck> (raw)
In-Reply-To: <20200507143547.GC1422@willie-the-truck>

On Thu, May 07, 2020 at 03:35:47PM +0100, Will Deacon wrote:
> On Thu, May 07, 2020 at 03:33:32PM +0100, Will Deacon wrote:
> > On Wed, May 06, 2020 at 08:51:27PM +0100, Mark Brown wrote:
> > > This patch series adds support for protecting the kernel and vDSO with
> > > BTI including code compiled with the BPF JIT at runtime.
> > > 
> > > We build the kernel with annotations for BTI and then map the kernel
> > > with GP based on the support on the boot CPU, rejecting secondaries that
> > > don't have BTI support. If there is a need to handle big.LITTLE systems
> > > with mismatched BTI support we will have to revisit this, currently no
> > > such implementations exist.
> > > 
> > > This series depends on several branches in the arm64 tree:
> > > 
> > >  - for-next/bti-user
> > >  - for-next/insn
> > >  - for-next/asm
> > > 
> > > v3:
> > >  - Add a patch adding a comment about why we enable leaf support for
> > >    PAC.
> > >  - Fix build of the 32 bit vDSO.
> > >  - Refactor the macro for emitting the ELF note for BTI code so that
> > >    the flags are defined separately in order to make it easier to
> > >    add handling for any future users.
> > 
> > Bugger, I'm still getting warnings (clang 11.0.1), but from an allmodconfig
> > build now:
> > 
> >   warning: some functions compiled with BTI and some compiled without BTI
> >   warning: not setting BTI in feature flags
> > 
> > (repeated many, many times).
> > 
> > I'll try to get you some more info.
> 
> Quick look at the log suggests that these are caused by HDRTEST, whatever
> that is.

Sorry, my parallel build threw me off, so I don't think it's HDRTEST after
all. One of the problems appears to be tracing:

    CC      kernel/trace/trace_clock.o
  warning: some functions compiled with BTI and some compiled without BTI
  warning: not setting BTI in feature flags

Looking at objdump, there are funny gcov functions with PACISAP prologues:

0000000000023e40 <__llvm_gcov_writeout>:
   23e40:       a9be57fe        stp     x30, x21, [sp, #-32]!
   23e44:       a9014ff4        stp     x20, x19, [sp, #16]
   23e48:       94000000        bl      0 <__sanitizer_cov_trace_pc>
   23e4c:       90000000        adrp    x0, 0 <__register_ftrace_function>
   23e50:       90000001        adrp    x1, 0 <__register_ftrace_function>
   23e54:       5293ac02        mov     w2, #0x9d60                     // #40288
   23e58:       91000000        add     x0, x0, #0x0
   [...]

:/

Will

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