Messages in this thread | | | Subject | Re: [RFC][PATCH 7/8] x86/mm/vsyscall: consider vsyscall page part of user address space | From | Andy Lutomirski <> | Date | Fri, 7 Sep 2018 15:58:19 -0700 |
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> On Sep 7, 2018, at 12:49 PM, Dave Hansen <dave.hansen@linux.intel.com> wrote: > > > From: Dave Hansen <dave.hansen@linux.intel.com> > > The vsyscall page is weird. It is in what is traditionally part of the > kernel address space. But, it has user permissions and we handle faults > on it like we would on a user page: interrupts on. > > Right now, we handle vsyscall emulation in the "bad_area" code, which > is used for both user-address-space and kernel-address-space faults. Move > the handling to the user-address-space code *only* and ensure we get there > by "excluding" the vsyscall page from the kernel address space via a check > in fault_in_kernel_space().
I assume the motivation is that you want to simplify the kernel error path. If so, can you mention this?
The patch itself is Reviewed-by: Andy Lutomirski <luto@kernel.org>, although adding an unlikely() somewhere might be nice.
> > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Sean Christopherson <sean.j.christopherson@intel.com> > Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: x86@kernel.org > Cc: Andy Lutomirski <luto@kernel.org> > --- > > b/arch/x86/mm/fault.c | 36 ++++++++++++++++++++++++------------ > 1 file changed, 24 insertions(+), 12 deletions(-) > > diff -puN arch/x86/mm/fault.c~vsyscall-is-user-address-space arch/x86/mm/fault.c > --- a/arch/x86/mm/fault.c~vsyscall-is-user-address-space 2018-09-07 11:21:48.720751896 -0700 > +++ b/arch/x86/mm/fault.c 2018-09-07 11:21:48.724751896 -0700 > @@ -873,18 +873,6 @@ __bad_area_nosemaphore(struct pt_regs *r > if (is_errata100(regs, address)) > return; > > -#ifdef CONFIG_X86_64 > - /* > - * Instruction fetch faults in the vsyscall page might need > - * emulation. > - */ > - if (unlikely((error_code & X86_PF_INSTR) && > - is_vsyscall_vaddr(address))) { > - if (emulate_vsyscall(regs, address)) > - return; > - } > -#endif > - > /* > * To avoid leaking information about the kernel page table > * layout, pretend that user-mode accesses to kernel addresses > @@ -1192,6 +1180,13 @@ access_error(unsigned long error_code, s > > static int fault_in_kernel_space(unsigned long address) > { > + /* > + * The vsyscall page is at an address above TASK_SIZE_MAX, > + * but is not considered part of the kernel address space. > + */ > + if (is_vsyscall_vaddr(address)) > + return false; > + > return address >= TASK_SIZE_MAX; > } > > @@ -1357,6 +1352,23 @@ void do_user_addr_space_fault(struct pt_ > if (sw_error_code & X86_PF_INSTR) > flags |= FAULT_FLAG_INSTRUCTION; > > +#ifdef CONFIG_X86_64 > + /* > + * Instruction fetch faults in the vsyscall page might need > + * emulation. The vsyscall page is at a high address > + * (>PAGE_OFFSET), but is considered to be part of the user > + * address space. > + * > + * The vsyscall page does not have a "real" VMA, so do this > + * emulation before we go searching for VMAse > + */ > + if (unlikely((sw_error_code & X86_PF_INSTR) && > + is_vsyscall_vaddr(address))) { > + if (emulate_vsyscall(regs, address)) > + return; > + } > +#endif > + > /* > * Kernel-mode access to the user address space should only occur > * inside well-defined areas of code listed in the exception > _
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