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Date: Thu, 6 Dec 2018 11:11:07 +0000
From: Will Deacon <will.deacon@....com>
To: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Catalin Marinas <catalin.marinas@....com>,
Christoph Lameter <cl@...ux.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mark Rutland <mark.rutland@....com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Marc Zyngier <marc.zyngier@....com>,
Dave Martin <dave.martin@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Ingo Molnar <mingo@...nel.org>,
Paul Lawrence <paullawrence@...gle.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Arnd Bergmann <arnd@...db.de>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Kate Stewart <kstewart@...uxfoundation.org>,
Mike Rapoport <rppt@...ux.vnet.ibm.com>,
kasan-dev <kasan-dev@...glegroups.com>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
linux-sparse@...r.kernel.org,
Linux Memory Management List <linux-mm@...ck.org>,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
Kostya Serebryany <kcc@...gle.com>,
Evgenii Stepanov <eugenis@...gle.com>,
Lee Smith <Lee.Smith@....com>,
Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
Jacob Bramley <Jacob.Bramley@....com>,
Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
Jann Horn <jannh@...gle.com>,
Mark Brand <markbrand@...gle.com>,
Chintan Pandya <cpandya@...eaurora.org>,
Vishwath Mohan <vishwath@...gle.com>
Subject: Re: [PATCH v12 20/25] kasan, arm64: add brk handler for inline
instrumentation
On Thu, Dec 06, 2018 at 11:31:43AM +0100, Andrey Konovalov wrote:
> On Thu, Nov 29, 2018 at 7:01 PM Will Deacon <will.deacon@....com> wrote:
> >
> > On Tue, Nov 27, 2018 at 05:55:38PM +0100, Andrey Konovalov wrote:
> > > Tag-based KASAN inline instrumentation mode (which embeds checks of shadow
> > > memory into the generated code, instead of inserting a callback) generates
> > > a brk instruction when a tag mismatch is detected.
> > >
> > > This commit adds a tag-based KASAN specific brk handler, that decodes the
> > > immediate value passed to the brk instructions (to extract information
> > > about the memory access that triggered the mismatch), reads the register
> > > values (x0 contains the guilty address) and reports the bug.
> > >
> > > Reviewed-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> > > Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
> > > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > > ---
> > > arch/arm64/include/asm/brk-imm.h | 2 +
> > > arch/arm64/kernel/traps.c | 68 +++++++++++++++++++++++++++++++-
> > > include/linux/kasan.h | 3 ++
> > > 3 files changed, 71 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
> > > index ed693c5bcec0..2945fe6cd863 100644
> > > --- a/arch/arm64/include/asm/brk-imm.h
> > > +++ b/arch/arm64/include/asm/brk-imm.h
> > > @@ -16,10 +16,12 @@
> > > * 0x400: for dynamic BRK instruction
> > > * 0x401: for compile time BRK instruction
> > > * 0x800: kernel-mode BUG() and WARN() traps
> > > + * 0x9xx: tag-based KASAN trap (allowed values 0x900 - 0x9ff)
> > > */
> > > #define FAULT_BRK_IMM 0x100
> > > #define KGDB_DYN_DBG_BRK_IMM 0x400
> > > #define KGDB_COMPILED_DBG_BRK_IMM 0x401
> > > #define BUG_BRK_IMM 0x800
> > > +#define KASAN_BRK_IMM 0x900
> > >
> > > #endif
> > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> > > index 5f4d9acb32f5..04bdc53716ef 100644
> > > --- a/arch/arm64/kernel/traps.c
> > > +++ b/arch/arm64/kernel/traps.c
> > > @@ -35,6 +35,7 @@
> > > #include <linux/sizes.h>
> > > #include <linux/syscalls.h>
> > > #include <linux/mm_types.h>
> > > +#include <linux/kasan.h>
> > >
> > > #include <asm/atomic.h>
> > > #include <asm/bug.h>
> > > @@ -284,10 +285,14 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
> > > }
> > > }
> > >
> > > -void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> > > +void __arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> > > {
> > > regs->pc += size;
> > > +}
> > >
> > > +void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> > > +{
> > > + __arm64_skip_faulting_instruction(regs, size);
> > > /*
> > > * If we were single stepping, we want to get the step exception after
> > > * we return from the trap.
> > > @@ -959,7 +964,7 @@ static int bug_handler(struct pt_regs *regs, unsigned int esr)
> > > }
> > >
> > > /* If thread survives, skip over the BUG instruction and continue: */
> > > - arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
> > > + __arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
> >
> > Why do you want to avoid the single-step logic here? Given that we're
> > skipping over the brk instruction, why wouldn't you want that to trigger
> > a step exception if single-step is enabled?
>
> I was asked to do that, see the discussion here:
>
> https://www.spinics.net/lists/linux-mm/msg146575.html
> https://www.spinics.net/lists/linux-mm/msg148215.html
> https://www.spinics.net/lists/linux-mm/msg148367.html
Aha, but we subsequently fixed the underlying problem in commit
9478f1927e6e ("arm64: only advance singlestep for user instruction traps").
You were on cc, but I appreciate it's not clear that it was related to this.
Anyway, you can just call arm64_skip_faulting_instruction() as you were
doing and there's no need for this refactoring.
Please could you spin a new version so that akpm can replace the one which
he has queued?
Thanks,
Will
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