linux-kernel - Re: [PATCH 6/8] riscv: add STRICT_KERNEL

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Date:   Thu, 5 Mar 2020 12:08:21 +0800
From:   Zong Li <zongbox@...il.com>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Zong Li <zong.li@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH 6/8] riscv: add STRICT_KERNEL_RWX support

Palmer Dabbelt <palmer@...belt.com> 於 2020年3月5日 週四 上午9:22寫道：
>
> On Mon, 17 Feb 2020 00:32:21 PST (-0800), zong.li@...ive.com wrote:
> > The commit contains that make text section as non-writable, rodata
> > section as read-only, and data section as non-executable.
> >
> > The init section should be changed to non-executable.
> >
> > Signed-off-by: Zong Li <zong.li@...ive.com>
> > ---
> >  arch/riscv/Kconfig                  |  1 +
> >  arch/riscv/include/asm/set_memory.h |  8 +++++
> >  arch/riscv/mm/init.c                | 45 +++++++++++++++++++++++++++++
> >  3 files changed, 54 insertions(+)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index f524d7e60648..308a4dbc0b39 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -62,6 +62,7 @@ config RISCV
> >       select ARCH_HAS_GIGANTIC_PAGE
> >       select ARCH_HAS_SET_DIRECT_MAP
> >       select ARCH_HAS_SET_MEMORY
> > +     select ARCH_HAS_STRICT_KERNEL_RWX
> >       select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
> >       select SPARSEMEM_STATIC if 32BIT
> >       select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
> > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> > index a91f192063c2..d3076087cb34 100644
> > --- a/arch/riscv/include/asm/set_memory.h
> > +++ b/arch/riscv/include/asm/set_memory.h
> > @@ -15,6 +15,14 @@ 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);
> >
> > +#ifdef CONFIG_STRICT_KERNEL_RWX
> > +void set_kernel_text_ro(void);
> > +void set_kernel_text_rw(void);
> > +#else
> > +static inline void set_kernel_text_ro(void) { }
> > +static inline void set_kernel_text_rw(void) { }
> > +#endif
> > +
> >  int set_direct_map_invalid_noflush(struct page *page);
> >  int set_direct_map_default_noflush(struct page *page);
> >
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 965a8cf4829c..09fa643e079c 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -12,11 +12,13 @@
> >  #include <linux/sizes.h>
> >  #include <linux/of_fdt.h>
> >  #include <linux/libfdt.h>
> > +#include <linux/set_memory.h>
> >
> >  #include <asm/fixmap.h>
> >  #include <asm/tlbflush.h>
> >  #include <asm/sections.h>
> >  #include <asm/pgtable.h>
> > +#include <asm/ptdump.h>
> >  #include <asm/io.h>
> >
> >  #include "../kernel/head.h"
> > @@ -477,6 +479,49 @@ static void __init setup_vm_final(void)
> >       csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE);
> >       local_flush_tlb_all();
> >  }
> > +
> > +#ifdef CONFIG_STRICT_KERNEL_RWX
> > +void set_kernel_text_rw(void)
> > +{
> > +     unsigned long text_start = (unsigned long)_text;
> > +     unsigned long text_end = (unsigned long)_etext;
> > +
> > +     set_memory_rw(text_start, (text_end - text_start) >> PAGE_SHIFT);
> > +}
> > +
> > +void set_kernel_text_ro(void)
> > +{
> > +     unsigned long text_start = (unsigned long)_text;
> > +     unsigned long text_end = (unsigned long)_etext;
> > +
> > +     set_memory_ro(text_start, (text_end - text_start) >> PAGE_SHIFT);
> > +}
> > +
> > +void mark_rodata_ro(void)
> > +{
> > +     unsigned long text_start = (unsigned long)_text;
> > +     unsigned long text_end = (unsigned long)_etext;
> > +     unsigned long rodata_start = (unsigned long)__start_rodata;
> > +     unsigned long data_start = (unsigned long)_sdata;
> > +     unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
> > +
> > +     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);
>
> Ya, this'll risk barfing because of srodata.

It might be OK because the range includes .rodata, .srodata and
__ex_table sections, but I need another symbol instead of _sdata as
you mentioned in other patch.

>
> > +     set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
> > +}
> > +#endif
> > +
> > +void free_initmem(void)
> > +{
> > +     unsigned long init_begin = (unsigned long)__init_begin;
> > +     unsigned long init_end = (unsigned long)__init_end;
> > +
> > +     /* Make the region as non-execuatble. */
> > +     set_memory_nx(init_begin, (init_end - init_begin) >> PAGE_SHIFT);
> > +     free_initmem_default(POISON_FREE_INITMEM);
> > +}
> > +
> >  #else
> >  asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >  {
>