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In-Reply-To: <e4bd592e-2e35-9c73-854e-1380222f34ef@csgroup.eu>
From: Jordan Niethe <jniethe5@gmail.com>
Date: Fri, 15 May 2020 13:46:02 +1000
Message-ID: <CACzsE9ojewbMn31zqm_XK3zfNtE7Ai2XTiFTgUNY+jWhfhpF_w@mail.gmail.com>
Subject: Re: [PATCH v8 13/30] powerpc: Add a probe_user_read_inst() function
To: Christophe Leroy <christophe.leroy@csgroup.eu>
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Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
 Alistair Popple <alistair@popple.id.au>, Nicholas Piggin <npiggin@gmail.com>,
 Balamuruhan S <bala24@linux.ibm.com>, naveen.n.rao@linux.vnet.ibm.com,
 linuxppc-dev@lists.ozlabs.org, Daniel Axtens <dja@axtens.net>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On Thu, May 14, 2020 at 3:46 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 06/05/2020 =C3=A0 05:40, Jordan Niethe a =C3=A9crit :
> > Introduce a probe_user_read_inst() function to use in cases where
> > probe_user_read() is used for getting an instruction. This will be more
> > useful for prefixed instructions.
> >
> > Reviewed-by: Alistair Popple <alistair@popple.id.au>
> > Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> > ---
> > v6: - New to series
> > ---
> >   arch/powerpc/include/asm/inst.h |  3 +++
> >   arch/powerpc/lib/Makefile       |  2 +-
> >   arch/powerpc/lib/inst.c         | 18 ++++++++++++++++++
> >   arch/powerpc/mm/fault.c         |  2 +-
> >   4 files changed, 23 insertions(+), 2 deletions(-)
> >   create mode 100644 arch/powerpc/lib/inst.c
> >
> > diff --git a/arch/powerpc/include/asm/inst.h b/arch/powerpc/include/asm=
/inst.h
> > index 552e953bf04f..3e9a58420151 100644
> > --- a/arch/powerpc/include/asm/inst.h
> > +++ b/arch/powerpc/include/asm/inst.h
> > @@ -37,4 +37,7 @@ static inline bool ppc_inst_equal(struct ppc_inst x, =
struct ppc_inst y)
> >       return ppc_inst_val(x) =3D=3D ppc_inst_val(y);
> >   }
> >
> > +int probe_user_read_inst(struct ppc_inst *inst,
> > +                      struct ppc_inst *nip);
> > +
> >   #endif /* _ASM_INST_H */
> > diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
> > index b8de3be10eb4..546591848219 100644
> > --- a/arch/powerpc/lib/Makefile
> > +++ b/arch/powerpc/lib/Makefile
> > @@ -16,7 +16,7 @@ CFLAGS_code-patching.o +=3D -DDISABLE_BRANCH_PROFILIN=
G
> >   CFLAGS_feature-fixups.o +=3D -DDISABLE_BRANCH_PROFILING
> >   endif
> >
> > -obj-y +=3D alloc.o code-patching.o feature-fixups.o pmem.o
> > +obj-y +=3D alloc.o code-patching.o feature-fixups.o pmem.o inst.o
> >
> >   ifndef CONFIG_KASAN
> >   obj-y       +=3D      string.o memcmp_$(BITS).o
> > diff --git a/arch/powerpc/lib/inst.c b/arch/powerpc/lib/inst.c
> > new file mode 100644
> > index 000000000000..eaf786afad2b
> > --- /dev/null
> > +++ b/arch/powerpc/lib/inst.c
> > @@ -0,0 +1,18 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + *  Copyright 2020, IBM Corporation.
> > + */
> > +
> > +#include <linux/uaccess.h>
> > +#include <asm/inst.h>
> > +
> > +int probe_user_read_inst(struct ppc_inst *inst,
> > +                      struct ppc_inst *nip)
> > +{
> > +     unsigned int val;
> > +     int err;
> > +
> > +     err =3D probe_user_read(&val, nip, sizeof(val));
> > +     *inst =3D ppc_inst(val);
> > +     return err;
> > +}
> > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> > index 4a50f125ec18..f3a943eae305 100644
> > --- a/arch/powerpc/mm/fault.c
> > +++ b/arch/powerpc/mm/fault.c
> > @@ -281,7 +281,7 @@ static bool bad_stack_expansion(struct pt_regs *reg=
s, unsigned long address,
> >                   access_ok(nip, sizeof(*nip))) {
> >                       struct ppc_inst inst;
> >
> > -                     if (!probe_user_read(&inst, nip, sizeof(inst)))
> > +                     if (!probe_user_read_inst(&inst, (struct ppc_inst=
 __user *)nip))
>
> Shouldn't 'nip' become de 'struct ppc_inst __user *' instead of casting ?
>
> >                               return !store_updates_sp(inst);
> >                       *must_retry =3D true;
> >               }
> >
Yeah it would make more sense to do it like this.
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -256,7 +256,7 @@ static bool bad_stack_expansion(struct pt_regs
*regs, unsigned long address,
      * expand to 1MB without further checks.
      */
     if (address + 0x100000 < vma->vm_end) {
-        unsigned int __user *nip =3D (unsigned int __user *)regs->nip;
+        struct ppc_inst __user *nip =3D (struct ppc_inst __user *)regs->ni=
p;
         /* get user regs even if this fault is in kernel mode */
         struct pt_regs *uregs =3D current->thread.regs;
         if (uregs =3D=3D NULL)
@@ -281,7 +281,7 @@ static bool bad_stack_expansion(struct pt_regs
*regs, unsigned long address,
             access_ok(nip, sizeof(*nip))) {
             struct ppc_inst inst;

-            if (!probe_user_read_inst(&inst, (struct ppc_inst __user *)nip=
))
+            if (!probe_user_read_inst(&inst, nip))
                 return !store_updates_sp(inst);
             *must_retry =3D true;
         }
--=20
2.17.1
>
> Christophe