Messages in this thread | | | Subject | Re: [PATCH v2 7/7] ARM: mm: Fix PXN process with LPAE feature | From | Kefeng Wang <> | Date | Mon, 7 Jun 2021 16:32:55 +0800 |
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Hi Russell, any comments, thanks.
On 2021/6/3 17:38, Kefeng Wang wrote: > > 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 == FS_L2_PERM ) > + 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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