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    SubjectRe: [PATCH v2 7/7] ARM: mm: Fix PXN process with LPAE feature
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    On 2021/6/2 23:58, Russell King (Oracle) wrote:
    > On Wed, Jun 02, 2021 at 11:13:14PM +0800, Kefeng Wang wrote:
    >>   IFSR format when using the Short-descriptor translation table format
    >>
    >>     Domain fault      01001            First level   01011     Second level
    >>
    >>     Permission fault 01101            First level   01111     Second level
    >>
    >>   IFSR format when using the Long-descriptor translation table format
    >>
    >>    0011LL Permission fault. LL bits indicate levelb.
    >>
    >> After check the ARM spec, I think for the permission fault,  we should panic
    >> with or without LPAE, will change to
    > As I explained in one of the previous patches, the page tables that get
    > used for mapping kernel space are the _tasks_ own page tables. Any new
    > kernel mappings are lazily copied to the task page tables - such as
    > when a module is loaded.
    >
    > The first time we touch a page, we could end up with a page translation
    > fault. This will call do_page_fault(), and so with your proposal,
    > loading a module will potentially cause a kernel panic in this case,
    > probably leading to systems that panic early during userspace boot.

    Could we add some FSR_FS check, only panic when the permission fault, eg,

    +static inline bool is_permission_fault(unsigned int fsr)
    +{
    +       int fs = fsr_fs(fsr);
    +#ifdef CONFIG_ARM_LPAE
    +       if ((fs & FS_PERM_NOLL_MASK) == FS_PERM_NOLL)
    +               return true;
    +#else
    +       if (fs == FS_L1_PERM || fs == )
    +               return true;
    +#endif
    +       return false;
    +}
    +
     static int __kprobes
     do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
     {
    @@ -255,8 +268,7 @@ do_page_fault(unsigned long addr, unsigned int fsr,
    struct pt_regs *regs)

            if (fsr & FSR_LNX_PF) {
                    vm_flags = VM_EXEC;
    -
    -               if (!user_mode(regs))
    +               if (is_permission_fault && !user_mode(regs))
                            die_kernel_fault("execution of memory",
                                             mm, addr, fsr, regs);
            }
    diff --git a/arch/arm/mm/fault.h b/arch/arm/mm/fault.h
    index 9ecc2097a87a..187954b4acca 100644
    --- a/arch/arm/mm/fault.h
    +++ b/arch/arm/mm/fault.h
    @@ -14,6 +14,8 @@

     #ifdef CONFIG_ARM_LPAE
     #define FSR_FS_AEA             17
    +#define FS_PERM_NOLL           0xC
    +#define FS_PERM_NOLL_MASK      0x3C

     static inline int fsr_fs(unsigned int fsr)
     {
    @@ -21,6 +23,8 @@ static inline int fsr_fs(unsigned int fsr)
     }
     #else
     #define FSR_FS_AEA             22
    +#define FS_L1_PERM             0xD
    +#define FS_L2_PERM             0xF

    and suggestion or proper solution to solve the issue?

    >
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      Last update: 2021-06-03 11:39    [W:3.222 / U:0.020 seconds]
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