Re: [PATCH v2 3/6] RISC-V: Enforce protections for kernel sections early

[Atish Patra]

On Tue, Oct 27, 2020 at 3:01 AM Mike Rapoport <rppt@xxxxxxxxxx> wrote:
>
> On Mon, Oct 26, 2020 at 04:02:51PM -0700, Atish Patra wrote:
> > Currently, all memblocks are mapped with PAGE_KERNEL_EXEC and the strict
> > permissions are only enforced after /init starts. This leaves the kernel
> > vulnerable from possible buggy built-in modules.
> >
> > Apply permissions to individual sections as early as possible.
> >
> > Signed-off-by: Atish Patra <atish.patra@xxxxxxx>
> > ---
> >  arch/riscv/include/asm/set_memory.h |  2 ++
> >  arch/riscv/kernel/setup.c           |  2 ++
> >  arch/riscv/mm/init.c                | 11 +++++++++--
> >  3 files changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> > index 4c5bae7ca01c..4cc3a4e2afd3 100644
> > --- a/arch/riscv/include/asm/set_memory.h
> > +++ b/arch/riscv/include/asm/set_memory.h
> > @@ -15,11 +15,13 @@ 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);
> > +void protect_kernel_text_data(void);
> >  #else
> >  static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
> >  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) {};
> >  #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 7d6a04ae3929..b722c5bf892c 100644
> > --- a/arch/riscv/kernel/setup.c
> > +++ b/arch/riscv/kernel/setup.c
> > @@ -22,6 +22,7 @@
> >  #include <asm/cpu_ops.h>
> >  #include <asm/early_ioremap.h>
> >  #include <asm/setup.h>
> > +#include <asm/set_memory.h>
> >  #include <asm/sections.h>
> >  #include <asm/sbi.h>
> >  #include <asm/tlbflush.h>
> > @@ -92,6 +93,7 @@ void __init setup_arch(char **cmdline_p)
> >  #if IS_ENABLED(CONFIG_RISCV_SBI)
> >       sbi_init();
> >  #endif
> > +     protect_kernel_text_data();
> >  #ifdef CONFIG_SWIOTLB
> >       swiotlb_init(1);
> >  #endif
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index ea933b789a88..5f196f8158d4 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -608,7 +608,7 @@ static inline void setup_vm_final(void)
> >  #endif /* CONFIG_MMU */
> >
> >  #ifdef CONFIG_STRICT_KERNEL_RWX
> > -void mark_rodata_ro(void)
> > +void protect_kernel_text_data(void)
> >  {
> >       unsigned long text_start = (unsigned long)_text;
> >       unsigned long text_end = (unsigned long)_etext;
> > @@ -617,9 +617,16 @@ void mark_rodata_ro(void)
> >       unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
> >
>
> A comment about that rodata permissions are set later would be nice
> here.
>

Sure. I will add that.

> >       set_memory_ro(text_start, (text_end - text_start) >> PAGE_SHIFT);
> > -     set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> >       set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> >       set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
> > +}
> > +
> > +void mark_rodata_ro(void)
> > +{
> > +     unsigned long rodata_start = (unsigned long)__start_rodata;
> > +     unsigned long data_start = (unsigned long)_data;
> > +
> > +     set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> >
> >       debug_checkwx();
> >  }
> > --
> > 2.25.1
> >
>
> --
> Sincerely yours,
> Mike.
>
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-- 
Regards,
Atish