Re: [Xen-devel] [PATCH 07/13] xen/arm: Simplify alternative patching

[Julien Grall]

On Fri, 25 May 2018, 22:54 Stefano Stabellini, <sstabell...@kernel.org>
wrote:

> You might want to CC Konrad next time on this patch
>

May I ask why? This code falls under Arm maintainership.

Cheers,


> On Tue, 22 May 2018, Julien Grall wrote:
> > This is part of XSA-263.
> >
> > Signed-off-by: Julien Grall <julien.gr...@arm.com>
> >
> > ---
> >     I am aware of the missing commit message here. I wanted to send the
> >     series on the ML to get some feedback first.
> > ---
> >  xen/arch/arm/alternative.c | 35 +++++++++++++----------------------
> >  1 file changed, 13 insertions(+), 22 deletions(-)
> >
> > diff --git a/xen/arch/arm/alternative.c b/xen/arch/arm/alternative.c
> > index 9ffdc475d6..bd62183def 100644
> > --- a/xen/arch/arm/alternative.c
> > +++ b/xen/arch/arm/alternative.c
> > @@ -97,12 +97,16 @@ static u32 get_alt_insn(const struct alt_instr *alt,
> >  /*
> >   * The region patched should be read-write to allow __apply_alternatives
> >   * to replacing the instructions when necessary.
> > + *
> > + * @update_offset: Offset between the region patched and the writable
> > + * region for the update. 0 if the patched region is writable.
> >   */
> > -static int __apply_alternatives(const struct alt_region *region)
> > +static int __apply_alternatives(const struct alt_region *region,
> > +                                paddr_t update_offset)
> >  {
> >      const struct alt_instr *alt;
> > -    const u32 *replptr;
> > -    u32 *origptr;
> > +    const u32 *replptr, *origptr;
> > +    u32 *updptr;
> >
> >      printk(XENLOG_INFO "alternatives: Patching with alt table %p ->
> %p\n",
> >             region->begin, region->end);
> > @@ -118,6 +122,7 @@ static int __apply_alternatives(const struct
> alt_region *region)
> >          BUG_ON(alt->alt_len != alt->orig_len);
> >
> >          origptr = ALT_ORIG_PTR(alt);
> > +        updptr = (void *)origptr + update_offset;
> >          replptr = ALT_REPL_PTR(alt);
> >
> >          nr_inst = alt->alt_len / sizeof(insn);
> > @@ -125,7 +130,7 @@ static int __apply_alternatives(const struct
> alt_region *region)
> >          for ( i = 0; i < nr_inst; i++ )
> >          {
> >              insn = get_alt_insn(alt, origptr + i, replptr + i);
> > -            *(origptr + i) = cpu_to_le32(insn);
> > +            *(updptr + i) = cpu_to_le32(insn);
> >          }
> >
> >          /* Ensure the new instructions reached the memory and nuke */
> > @@ -162,9 +167,6 @@ static int __apply_alternatives_multi_stop(void
> *unused)
> >          paddr_t xen_size = _end - _start;
> >          unsigned int xen_order = get_order_from_bytes(xen_size);
> >          void *xenmap;
> > -        struct virtual_region patch_region = {
> > -            .list = LIST_HEAD_INIT(patch_region.list),
> > -        };
> >
> >          BUG_ON(patched);
> >
> > @@ -178,30 +180,19 @@ static int __apply_alternatives_multi_stop(void
> *unused)
> >          BUG_ON(!xenmap);
> >
> >          /*
> > -         * If we generate a new branch instruction, the target will be
> > -         * calculated in this re-mapped Xen region. So we have to
> register
> > -         * this re-mapped Xen region as a virtual region temporarily.
> > -         */
> > -        patch_region.start = xenmap;
> > -        patch_region.end = xenmap + xen_size;
> > -        register_virtual_region(&patch_region);
> > -
> > -        /*
> >           * Find the virtual address of the alternative region in the new
> >           * mapping.
> >           * alt_instr contains relative offset, so the function
> >           * __apply_alternatives will patch in the re-mapped version of
> >           * Xen.
> >           */
> > -        region.begin = (void *)__alt_instructions - (void *)_start +
> xenmap;
> > -        region.end = (void *)__alt_instructions_end - (void *)_start +
> xenmap;
> > +        region.begin = __alt_instructions;
> > +        region.end = __alt_instructions_end;
> >
> > -        ret = __apply_alternatives(&region);
> > +        ret = __apply_alternatives(&region, xenmap - (void *)_start);
> >          /* The patching is not expected to fail during boot. */
> >          BUG_ON(ret != 0);
> >
> > -        unregister_virtual_region(&patch_region);
> > -
> >          vunmap(xenmap);
> >
> >          /* Barriers provided by the cache flushing */
> > @@ -235,7 +226,7 @@ int apply_alternatives(const struct alt_instr
> *start, const struct alt_instr *en
> >          .end = end,
> >      };
> >
> > -    return __apply_alternatives(&region);
> > +    return __apply_alternatives(&region, 0);
> >  }
> >
> >  /*
> > --
> > 2.11.0
> >
>
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