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Date:   Wed, 27 Feb 2019 15:08:30 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com,
        julien.thierry@arm.com, will.deacon@arm.com, luto@amacapital.net,
        mingo@kernel.org, catalin.marinas@arm.com, james.morse@arm.com,
        valentin.schneider@arm.com, brgerst@gmail.com, jpoimboe@redhat.com,
        luto@kernel.org, bp@alien8.de, dvlasenk@redhat.com
Cc:     linux-kernel@vger.kernel.org, aryabinin@virtuozzo.com,
        glider@google.com, dvyukov@google.com
Subject: Re: [PATCH 5/6] objtool: Add UACCESS validation
Message-ID: <20190227140830.GP32494@hirez.programming.kicks-ass.net>
References: <20190225124330.613028745@infradead.org>
 <20190225125232.191698923@infradead.org>
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On Mon, Feb 25, 2019 at 01:43:35PM +0100, Peter Zijlstra wrote:
> It is important that UACCESS regions are as small as possible;
> furthermore the UACCESS state is not scheduled, so doing anything that
> might directly call into the scheduler will cause random code to be
> ran with UACCESS enabled.
> 
> Teach objtool too track UACCESS state and warn about any CALL made
> while UACCESS is enabled. This very much includes the __fentry__()
> tracing calls and __preempt_schedule() calls.
> 
> Note that exceptions _do_ save/restore the UACCESS state, and therefore
> they can drive preemption. This also means that all exception handlers
> must have an otherwise dedundant UACCESS disable instruction;
> therefore ignore this warning for !STT_FUNC code (exception handlers
> are not normal functions).
> 
> It also provides a UACCESS_SAFE() annotation which allows explicit
> annotation. This is meant to be used for future things like:
> unsafe_copy_{to,from}_user().
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

So KASAN is wildly unhappy..

I can't actually find any definitions of those functions, so I can't
very well mark the safe, even if we wanted to.

---

>> arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x59: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x6a: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x7b: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x8f: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0xa3: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0xb4: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0xc5: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0xdc: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0xf0: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x101: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x112: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x123: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x134: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x145: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x156: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x167: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x177: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x192: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x1bc: call to __asan_store8_noabort() with UACCESS enabled
>> arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x1f2: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x212: call to __asan_store8_noabort() with UACCESS enabled
>> arch/x86/kernel/signal.o: warning: objtool: restore_sigcontext()+0x1d8: call to force_valid_ss.isra.0() with UACCESS enabled
>> arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x3f: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x50: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x61: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x75: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x89: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x9a: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0xab: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0xbc: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0xcd: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0xde: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0xef: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x100: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x111: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x122: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x133: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x143: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x157: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x173: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x18e: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x1a8: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x1c2: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x1ee: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: setup_sigcontext()+0x217: call to __asan_load8_noabort() with UACCESS enabled
>> arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x618: call to __asan_load8_noabort() with UACCESS enabled
>> arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x630: call to __asan_loadN_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x681: call to __asan_load8_noabort() with UACCESS enabled
>> arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x6a0: call to __asan_load4_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x6bd: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x7cb: call to __asan_load8_noabort() with UACCESS enabled
>> arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x6dd: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x6f0: call to __asan_store8_noabort() with UACCESS enabled
>> arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x707: call to __asan_store4_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x2c6: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x2e3: call to __asan_loadN_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x334: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x352: call to __asan_load4_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x374: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x49d: call to __asan_load8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x393: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x3aa: call to __asan_store8_noabort() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: do_signal()+0x3c1: call to __asan_store4_noabort() with UACCESS enabled