Re: [PATCH v3] riscv: Fix permissions for all mm's during mm init

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On 02/09/2022 11:13, Vladimir Isaev wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> It is possible to have more than one mm (init_mm) during memory
> permission fixes. In my case it was caused by request_module
> from drivers/net/phy/phy_device.c and leads to following Oops
> during free_initmem() on RV32 platform:
>      Unable to handle kernel paging request at virtual address c0800000
>      Oops [#1]
>      Modules linked in:
>      CPU: 0 PID: 1 Comm: swapper Not tainted 5.15.45
>      Hardware name: Syntacore SCR5 SDK board (DT)
>      epc : __memset+0x58/0xf4
>       ra : free_reserved_area+0xfa/0x15a
>      epc : c02b26ac ra : c00eb588 sp : c1c1fed0
>       gp : c1898690 tp : c1c98000 t0 : c0800000
>       t1 : ffffffff t2 : 00000000 s0 : c1c1ff20
>       s1 : c189a000 a0 : c0800000 a1 : cccccccc
>       a2 : 00001000 a3 : c0801000 a4 : 00000000
>       a5 : 00800000 a6 : fef09000 a7 : 00000000
>       s2 : c0e57000 s3 : c10edcf8 s4 : 000000cc
>       s5 : ffffefff s6 : c188a9f4 s7 : 00000001
>       s8 : c0800000 s9 : fef1b000 s10: c10ee000
>       s11: c189a000 t3 : 00000000 t4 : 00000000
>       t5 : 00000000 t6 : 00000001
>      status: 00000120 badaddr: c0800000 cause: 0000000f
>      [<c0488658>] free_initmem+0x204/0x222
>      [<c048d05a>] kernel_init+0x32/0xfc
>      [<c0002f76>] ret_from_exception+0x0/0xc
>      ---[ end trace 7a5e2b002350b528 ]---
> 
> This is because request_module attempted to modprobe module, so it created
> new mm with the copy of kernel's page table. And this copy won't be updated
> in case of 4M pages and RV32 (pgd is the leaf).
> 
> To fix this we can update protection bits for all of existing mm-s, the
> same as ARM does, see commit 08925c2f124f
> ("ARM: 8464/1: Update all mm structures with section adjustments").
> 
> Fixes: 19a00869028f ("RISC-V: Protect all kernel sections including init early")
> Signed-off-by: Vladimir Isaev <vladimir.isaev@xxxxxxxxxxxxx>
> Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> ---
> Changes for v3:
>   - Add WARN_ON(state != SYSTEM_FREEING_INITMEM) to fix_kernel_mem_early()
>     to make sure that the function used only during permission fixes.
>   - Add comment to fix_kernel_mem_early().
> 
> Changes for v2:
>   - Fix commit message format.
>   - Add 'Fixes' tag.

Sweet, thanks.

Ran it through a 32bit build & been running with this applied on 64bit for
the afternoon & everything still seems to be intact. Therefore:
Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>

Thanks for you patch,
Conor.

> ---
>  arch/riscv/include/asm/set_memory.h | 20 ++--------
>  arch/riscv/kernel/setup.c           | 11 -----
>  arch/riscv/mm/init.c                | 29 +++++++++++---
>  arch/riscv/mm/pageattr.c            | 62 +++++++++++++++++++++++++----
>  4 files changed, 82 insertions(+), 40 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> index a2c14d4b3993..bb0f6b4ed86b 100644
> --- a/arch/riscv/include/asm/set_memory.h
> +++ b/arch/riscv/include/asm/set_memory.h
> @@ -16,28 +16,16 @@ 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_rw_nx(unsigned long addr, int numpages);
> -static __always_inline int set_kernel_memory(char *startp, char *endp,
> -                                            int (*set_memory)(unsigned long start,
> -                                                              int num_pages))
> -{
> -       unsigned long start = (unsigned long)startp;
> -       unsigned long end = (unsigned long)endp;
> -       int num_pages = PAGE_ALIGN(end - start) >> PAGE_SHIFT;
> -
> -       return set_memory(start, num_pages);
> -}
> +void fix_kernel_mem_early(char *startp, char *endp, pgprot_t set_mask,
> +                         pgprot_t clear_mask);
>  #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 int set_memory_rw_nx(unsigned long addr, int numpages) { return 0; }
> -static inline int set_kernel_memory(char *startp, char *endp,
> -                                   int (*set_memory)(unsigned long start,
> -                                                     int num_pages))
> -{
> -       return 0;
> -}
> +static inline void fix_kernel_mem_early(char *startp, char *endp,
> +                                       pgprot_t set_mask, pgprot_t clear_mask) { }
>  #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 95ef6e2bf45c..17eae1406092 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -27,7 +27,6 @@
>  #include <asm/early_ioremap.h>
>  #include <asm/pgtable.h>
>  #include <asm/setup.h>
> -#include <asm/set_memory.h>
>  #include <asm/sections.h>
>  #include <asm/sbi.h>
>  #include <asm/tlbflush.h>
> @@ -318,13 +317,3 @@ static int __init topology_init(void)
>         return 0;
>  }
>  subsys_initcall(topology_init);
> -
> -void free_initmem(void)
> -{
> -       if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
> -               set_kernel_memory(lm_alias(__init_begin), lm_alias(__init_end),
> -                                 IS_ENABLED(CONFIG_64BIT) ?
> -                                       set_memory_rw : set_memory_rw_nx);
> -
> -       free_initmem_default(POISON_FREE_INITMEM);
> -}
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index b56a0a75533f..978202712535 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -16,7 +16,6 @@
>  #include <linux/of_fdt.h>
>  #include <linux/of_reserved_mem.h>
>  #include <linux/libfdt.h>
> -#include <linux/set_memory.h>
>  #include <linux/dma-map-ops.h>
>  #include <linux/crash_dump.h>
>  #include <linux/hugetlb.h>
> @@ -28,6 +27,7 @@
>  #include <asm/io.h>
>  #include <asm/ptdump.h>
>  #include <asm/numa.h>
> +#include <asm/set_memory.h>
> 
>  #include "../kernel/head.h"
> 
> @@ -714,10 +714,14 @@ static __init pgprot_t pgprot_from_va(uintptr_t va)
> 
>  void mark_rodata_ro(void)
>  {
> -       set_kernel_memory(__start_rodata, _data, set_memory_ro);
> -       if (IS_ENABLED(CONFIG_64BIT))
> -               set_kernel_memory(lm_alias(__start_rodata), lm_alias(_data),
> -                                 set_memory_ro);
> +       pgprot_t set_mask = __pgprot(_PAGE_READ);
> +       pgprot_t clear_mask = __pgprot(_PAGE_WRITE);
> +
> +       fix_kernel_mem_early(__start_rodata, _data, set_mask, clear_mask);
> +       if (IS_ENABLED(CONFIG_64BIT)) {
> +               fix_kernel_mem_early(lm_alias(__start_rodata), lm_alias(_data),
> +                                    set_mask, clear_mask);
> +       }
> 
>         debug_checkwx();
>  }
> @@ -1243,3 +1247,18 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>         return vmemmap_populate_basepages(start, end, node, NULL);
>  }
>  #endif
> +
> +void free_initmem(void)
> +{
> +       pgprot_t set_mask = __pgprot(_PAGE_READ | _PAGE_WRITE);
> +       pgprot_t clear_mask = IS_ENABLED(CONFIG_64BIT) ?
> +                             __pgprot(0) : __pgprot(_PAGE_EXEC);
> +
> +       if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) {
> +               fix_kernel_mem_early(lm_alias(__init_begin),
> +                                    lm_alias(__init_end),
> +                                    set_mask, clear_mask);
> +       }
> +
> +       free_initmem_default(POISON_FREE_INITMEM);
> +}
> diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
> index 5e49e4b4a4cc..74b8107ac743 100644
> --- a/arch/riscv/mm/pageattr.c
> +++ b/arch/riscv/mm/pageattr.c
> @@ -5,6 +5,7 @@
> 
>  #include <linux/pagewalk.h>
>  #include <linux/pgtable.h>
> +#include <linux/sched.h>
>  #include <asm/tlbflush.h>
>  #include <asm/bitops.h>
>  #include <asm/set_memory.h>
> @@ -104,24 +105,69 @@ static const struct mm_walk_ops pageattr_ops = {
>         .pte_hole = pageattr_pte_hole,
>  };
> 
> -static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
> -                       pgprot_t clear_mask)
> +static int __set_memory_mm(struct mm_struct *mm, unsigned long start,
> +                          unsigned long end, pgprot_t set_mask,
> +                          pgprot_t clear_mask)
>  {
>         int ret;
> -       unsigned long start = addr;
> -       unsigned long end = start + PAGE_SIZE * numpages;
>         struct pageattr_masks masks = {
>                 .set_mask = set_mask,
>                 .clear_mask = clear_mask
>         };
> 
> +       mmap_read_lock(mm);
> +       ret = walk_page_range_novma(mm, start, end, &pageattr_ops, NULL,
> +                                   &masks);
> +       mmap_read_unlock(mm);
> +
> +       return ret;
> +}
> +
> +void fix_kernel_mem_early(char *startp, char *endp, pgprot_t set_mask,
> +                         pgprot_t clear_mask)
> +{
> +       struct task_struct *t, *s;
> +
> +       unsigned long start = (unsigned long)startp;
> +       unsigned long end = PAGE_ALIGN((unsigned long)endp);
> +
> +       /*
> +        * In the SYSTEM_FREEING_INITMEM state we expect that all async code
> +        * is done and no new userspace task can be created.
> +        * So rcu_read_lock() should be enough here.
> +        */
> +       WARN_ON(system_state != SYSTEM_FREEING_INITMEM);
> +
> +       __set_memory_mm(current->active_mm, start, end, set_mask, clear_mask);
> +       __set_memory_mm(&init_mm, start, end, set_mask, clear_mask);
> +
> +       rcu_read_lock();
> +       for_each_process(t) {
> +               if (t->flags & PF_KTHREAD)
> +                       continue;
> +               for_each_thread(t, s) {
> +                       if (s->mm) {
> +                               __set_memory_mm(s->mm, start, end, set_mask,
> +                                               clear_mask);
> +                       }
> +               }
> +       }
> +       rcu_read_unlock();
> +
> +       flush_tlb_kernel_range(start, end);
> +}
> +
> +static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
> +                       pgprot_t clear_mask)
> +{
> +       int ret;
> +       unsigned long start = addr;
> +       unsigned long end = start + PAGE_SIZE * numpages;
> +
>         if (!numpages)
>                 return 0;
> 
> -       mmap_read_lock(&init_mm);
> -       ret =  walk_page_range_novma(&init_mm, start, end, &pageattr_ops, NULL,
> -                                    &masks);
> -       mmap_read_unlock(&init_mm);
> +       ret = __set_memory_mm(&init_mm, start, end, set_mask, clear_mask);
> 
>         flush_tlb_kernel_range(start, end);
> 
> --
> 2.37.2
> 
> 
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