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

Atish Patra
2020-10-29T19:24:11Z

On Tue, Oct 27, 2020 at 3:46 AM Mike Rapoport <rppt@kernel.org> 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@wdc.com>
> > ---
> > 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.

> > +}
> > +
> > 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@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

--
Regards,
Atish