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
