Re: [PATCH V2] riscv: kexec: Fixup synchronization problem between init_mm and active_mm

[Guo Ren]

On Wed, Jul 12, 2023 at 10:43 AM Palmer Dabbelt <palmer@xxxxxxxxxxxx> wrote:
>
> On Tue, 11 Jul 2023 04:07:22 PDT (-0700), alex@xxxxxxxx wrote:
> > Hi Guo,
> >
> >
> > On 10/07/2023 07:40, guoren@xxxxxxxxxx wrote:
> >> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >>
> >> The machine_kexec() uses set_memory_x to modify the direct mapping
> >> attributes from RW to RWX. But set_memory_x only changes the init_mm's
> >> attributes, not current->active_mm, so when kexec jumps into
> >> control_buffer, the instruction page fault happens, and there is no
> >> minor_pagefault for it, then panic.
> >
> >
> > I think it needs more details like this:
> >
> > "The current implementation of set_memory_x does not split hugepages in
> > the linear mapping and then when a PGD mapping is used, the whole PGD is
> > marked as executable. But changing the permissions at the PGD level must
> > be propagated to all the page tables."
> >
> >
> >>
> >> The bug is found on an MMU_sv39 machine, and the direct mapping used a
> >> 1GB PUD, the pgd entries. Here is the bug output:
> >>
> >>   kexec_core: Starting new kernel
> >>   Will call new kernel at 00300000 from hart id 0
> >>   FDT image at 747c7000
> >>   Bye...
> >>   Unable to handle kernel paging request at virtual address ffffffda23b0d000
> >>   Oops [#1]
> >>   Modules linked in:
> >>   CPU: 0 PID: 53 Comm: uinit Not tainted 6.4.0-rc6 #15
> >>   Hardware name: Sophgo Mango (DT)
> >>   epc : 0xffffffda23b0d000
> >>    ra : machine_kexec+0xa6/0xb0
> >>   epc : ffffffda23b0d000 ra : ffffffff80008272 sp : ffffffc80c173d10
> >>    gp : ffffffff8150e1e0 tp : ffffffd9073d2c40 t0 : 0000000000000000
> >>    t1 : 0000000000000042 t2 : 6567616d69205444 s0 : ffffffc80c173d50
> >>    s1 : ffffffd9076c4800 a0 : ffffffd9076c4800 a1 : 0000000000300000
> >>    a2 : 00000000747c7000 a3 : 0000000000000000 a4 : ffffffd800000000
> >>    a5 : 0000000000000000 a6 : ffffffd903619c40 a7 : ffffffffffffffff
> >>    s2 : ffffffda23b0d000 s3 : 0000000000300000 s4 : 00000000747c7000
> >>    s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
> >>    s8 : 0000000000000000 s9 : 0000000000000000 s10: 0000000000000000
> >>    s11: 0000003f940001a0 t3 : ffffffff815351af t4 : ffffffff815351af
> >>    t5 : ffffffff815351b0 t6 : ffffffc80c173b50
> >>   status: 0000000200000100 badaddr: ffffffda23b0d000 cause: 000000000000000c
> >>
> >> The solution is to fix machine_kexec() to remap control code page outside
> >> the linear mapping.
> >
> >
> > "Given the current flaw in the set_memory_x implementation, the simplest
> > solution is to ..."
> >
> >
> >>
> >> Fixes: 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear mapping")
> >> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> >> Cc: Alexandre Ghiti <alex@xxxxxxxx>
> >> ---
> >> Changelog:
> >> V2:
> >>   - Use vm_map_ram instead of modifying set_memory_x
> >>   - Correct Fixes tag
> >> ---
> >>   arch/riscv/include/asm/kexec.h    |  1 +
> >>   arch/riscv/kernel/machine_kexec.c | 14 ++++++++++----
> >>   2 files changed, 11 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/arch/riscv/include/asm/kexec.h b/arch/riscv/include/asm/kexec.h
> >> index 2b56769cb530..17456e91476e 100644
> >> --- a/arch/riscv/include/asm/kexec.h
> >> +++ b/arch/riscv/include/asm/kexec.h
> >> @@ -41,6 +41,7 @@ crash_setup_regs(struct pt_regs *newregs,
> >>   struct kimage_arch {
> >>      void *fdt; /* For CONFIG_KEXEC_FILE */
> >>      unsigned long fdt_addr;
> >> +    void *control_code_buffer;
> >>   };
> >>
> >>   extern const unsigned char riscv_kexec_relocate[];
> >> diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
> >> index 2d139b724bc8..eeb209775107 100644
> >> --- a/arch/riscv/kernel/machine_kexec.c
> >> +++ b/arch/riscv/kernel/machine_kexec.c
> >> @@ -86,7 +86,14 @@ machine_kexec_prepare(struct kimage *image)
> >>
> >>      /* Copy the assembler code for relocation to the control page */
> >>      if (image->type != KEXEC_TYPE_CRASH) {
> >> -            control_code_buffer = page_address(image->control_code_page);
> >> +            control_code_buffer = vm_map_ram(&image->control_code_page,
> >> +                                             KEXEC_CONTROL_PAGE_SIZE/PAGE_SIZE,
> >> +                                             NUMA_NO_NODE);
> >> +            if (control_code_buffer == NULL) {
> >> +                    pr_err("Failed to vm_map control page\n");
> >> +                    return -ENOMEM;
> >> +            }
> >> +
> >>              control_code_buffer_sz = page_size(image->control_code_page);
> >>
> >>              if (unlikely(riscv_kexec_relocate_size > control_code_buffer_sz)) {
> >> @@ -97,8 +104,7 @@ machine_kexec_prepare(struct kimage *image)
> >>              memcpy(control_code_buffer, riscv_kexec_relocate,
> >>                      riscv_kexec_relocate_size);
> >>
> >> -            /* Mark the control page executable */
> >> -            set_memory_x((unsigned long) control_code_buffer, 1);
> >> +            internal->control_code_buffer = control_code_buffer;
> >
> >
> > Where is this mapping marked as executable? I see that vm_map_ram() maps
> > the pages as PAGE_KERNEL, which does not set PAGE_EXEC.
> >
> >
> >>      }
> >>
> >>      return 0;
> >> @@ -211,7 +217,7 @@ machine_kexec(struct kimage *image)
> >>      unsigned long this_cpu_id = __smp_processor_id();
> >>      unsigned long this_hart_id = cpuid_to_hartid_map(this_cpu_id);
> >>      unsigned long fdt_addr = internal->fdt_addr;
> >> -    void *control_code_buffer = page_address(image->control_code_page);
> >> +    void *control_code_buffer = internal->control_code_buffer;
> >>      riscv_kexec_method kexec_method = NULL;
> >>
> >>   #ifdef CONFIG_SMP
> >
> >
> > Otherwise, you can add:
> >
> > Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> >
> > Thanks,
> >
> > Alex
>
> Thanks for looking at this.  Guo: do you have a re-spit that fixes the
> issues Alex pointed out?  Sorry if I just missed it.
Sorry for the late reply. Here is the patch of v3:
https://lore.kernel.org/linux-riscv/20230713150758.2956316-1-guoren@xxxxxxxxxx/



-- 
Best Regards
 Guo Ren