Re: [PATCH v2 5/6] RISC-V: Protect .init.text & .init.data

[Mike Rapoport]

On Thu, Oct 29, 2020 at 12:21:41PM -0700, Atish Patra wrote:
> On Tue, Oct 27, 2020 at 3:46 AM Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> >
> > On Mon, Oct 26, 2020 at 04:02:53PM -0700, Atish Patra wrote:
> > > Currently, .init.text & .init.data are intermixed which makes it impossible
> > > apply different permissions to them. .init.data shouldn't need exec
> > > permissions while .init.text shouldn't have write permission.
> > >
> > > Keep them in separate sections so that different permissions are applied to
> > > each section. This improves the kernel protection under
> > > CONFIG_STRICT_KERNEL_RWX. We also need to restore the permissions for the
> > > entire _init section after it is freed so that those pages can be used for
> > > other purpose.
> > >
> > > Signed-off-by: Atish Patra <atish.patra@xxxxxxx>
> > > ---
> > >  arch/riscv/include/asm/sections.h   |  2 ++
> > >  arch/riscv/include/asm/set_memory.h |  2 ++
> > >  arch/riscv/kernel/setup.c           |  9 +++++
> > >  arch/riscv/kernel/vmlinux.lds.S     | 51 ++++++++++++++++-------------
> > >  arch/riscv/mm/init.c                |  8 ++++-
> > >  arch/riscv/mm/pageattr.c            |  6 ++++
> > >  6 files changed, 54 insertions(+), 24 deletions(-)
> > >
> > > diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
> > > index 3a9971b1210f..1595c5b60cfd 100644
> > > --- a/arch/riscv/include/asm/sections.h
> > > +++ b/arch/riscv/include/asm/sections.h
> > > @@ -9,5 +9,7 @@
> > >
> > >  extern char _start[];
> > >  extern char _start_kernel[];
> > > +extern char __init_data_begin[], __init_data_end[];
> > > +extern char __init_text_begin[], __init_text_end[];
> > >
> > >  #endif /* __ASM_SECTIONS_H */
> > > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> > > index 4cc3a4e2afd3..913429c9c1ae 100644
> > > --- a/arch/riscv/include/asm/set_memory.h
> > > +++ b/arch/riscv/include/asm/set_memory.h
> > > @@ -15,6 +15,7 @@ int set_memory_ro(unsigned long addr, int numpages);
> > >  int set_memory_rw(unsigned long addr, int numpages);
> > >  int set_memory_x(unsigned long addr, int numpages);
> > >  int set_memory_nx(unsigned long addr, int numpages);
> > > +int set_memory_default(unsigned long addr, int numpages);
> > >  void protect_kernel_text_data(void);
> > >  #else
> > >  static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
> > > @@ -22,6 +23,7 @@ static inline int set_memory_rw(unsigned long addr, int numpages) { return 0; }
> > >  static inline int set_memory_x(unsigned long addr, int numpages) { return 0; }
> > >  static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
> > >  static inline void protect_kernel_text_data(void) {};
> > > +static inline int set_memory_default(unsigned long addr, int numpages) { return 0; }
> > >  #endif
> > >
> > >  int set_direct_map_invalid_noflush(struct page *page);
> > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > > index b722c5bf892c..abfbdc8cfef3 100644
> > > --- a/arch/riscv/kernel/setup.c
> > > +++ b/arch/riscv/kernel/setup.c
> > > @@ -123,3 +123,12 @@ static int __init topology_init(void)
> > >       return 0;
> > >  }
> > >  subsys_initcall(topology_init);
> > > +
> > > +void free_initmem(void)
> > > +{
> > > +     unsigned long init_begin = (unsigned long)__init_begin;
> > > +     unsigned long init_end = (unsigned long)__init_end;
> > > +
> > > +     set_memory_default(init_begin, (init_end - init_begin) >> PAGE_SHIFT);
> >
> > And what does "default" imply?
> > Maybe set_memory_rw() would better name ...
> >
> > > +     free_initmem_default(POISON_FREE_INITMEM);
> > > +}
> >
> > ...
> >
> > > diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
> > > index 19fecb362d81..04f3fc16aa9c 100644
> > > --- a/arch/riscv/mm/pageattr.c
> > > +++ b/arch/riscv/mm/pageattr.c
> > > @@ -128,6 +128,12 @@ static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
> > >       return ret;
> > >  }
> > >
> > > +int set_memory_default(unsigned long addr, int numpages)
> > > +{
> > > +     return __set_memory(addr, numpages, __pgprot(_PAGE_KERNEL),
> > > +                         __pgprot(_PAGE_EXEC));
> >
> > ... because you'd need to find what _PAGE_KERNEL is, do bitwise ops and
> > than find out that default is apparently RW :)
> >
> 
> Yeah. But We have explicitly disable the EXECUTE bit as these pages were marked
> with RWX earlier. set_memory_rw makes sure that RW bits are set but
> doesn't disable
> the X bit.

Maybe set_memory_rw_nx() then?
Then there will be no ambiguity about what this function does.

Besides, having set_memory_default() and set_direct_map_default() with
different masks would be confusing :)

> > > +}
> > > +
> > >  int set_memory_ro(unsigned long addr, int numpages)
> > >  {
> > >       return __set_memory(addr, numpages, __pgprot(_PAGE_READ),
> > > --
> > > 2.25.1
> > >
> >
> > --
> > Sincerely yours,
> > Mike.
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> 
> 
> 
> -- 
> Regards,
> Atish

-- 
Sincerely yours,
Mike.