Re: [PATCH v8 13/30] powerpc: Add a probe_user_read_inst() function

[Jordan Niethe <jniethe5@gmail.com>]

On Thu, May 14, 2020 at 3:46 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 06/05/2020 à 05:40, Jordan Niethe a écrit :
> > 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) == 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 += -DDISABLE_BRANCH_PROFILING
> >   CFLAGS_feature-fixups.o += -DDISABLE_BRANCH_PROFILING
> >   endif
> >
> > -obj-y += alloc.o code-patching.o feature-fixups.o pmem.o
> > +obj-y += alloc.o code-patching.o feature-fixups.o pmem.o inst.o
> >
> >   ifndef CONFIG_KASAN
> >   obj-y       +=      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 = probe_user_read(&val, nip, sizeof(val));
> > +     *inst = 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 *regs, 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 = 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 = (unsigned int __user *)regs->nip;
+        struct ppc_inst __user *nip = (struct ppc_inst __user *)regs->nip;
         /* get user regs even if this fault is in kernel mode */
         struct pt_regs *uregs = current->thread.regs;
         if (uregs == 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 = true;
         }
-- 
2.17.1
>
> Christophe