On Mon, Feb 01, 2021 at 01:03:45PM +0000, Russell King - ARM Linux admin wrote:
> On Mon, Feb 01, 2021 at 12:47:20PM +0000, Mark Rutland wrote:
> > 1. copy reloc code into buffer
> > 2. alter variables in copy of reloc code
> > 3. branch to buffer
> >
> > ... which would avoid this class of problem too.
>
> Yep, slightly messy to do though:
>
> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
> index 5d84ad333f05..6058e0d3a40d 100644
> --- a/arch/arm/kernel/machine_kexec.c
> +++ b/arch/arm/kernel/machine_kexec.c
> @@ -174,18 +174,27 @@ void machine_kexec(struct kimage *image)
>
> reboot_code_buffer = page_address(image->control_code_page);
>
> - /* Prepare parameters for reboot_code_buffer*/
> - set_kernel_text_rw();
> - kexec_start_address = image->start;
> - kexec_indirection_page = page_list;
> - kexec_mach_type = machine_arch_type;
> - kexec_boot_atags = image->arch.kernel_r2;
> -
> /* copy our kernel relocation code to the control code page */
> reboot_entry = fncpy(reboot_code_buffer,
> &relocate_new_kernel,
> relocate_new_kernel_size);
>
> +#define set(what, val) \
> + do { \
> + uintptr_t __funcp_address; \
> + int __offset; \
> + void *__ptr; \
> + asm("" : "=r" (__funcp_address) : "0" (&relocate_new_kernel)); \
> + __offset = (uintptr_t)&(what) - (__funcp_address & ~1); \
> + __ptr = reboot_code_buffer + __offset; \
> + *(__typeof__(&(what)))__ptr = val; \
> + } while (0)
> +
> + set(kexec_start_address, image->start);
> + set(kexec_indirection_page, page_list);
> + set(kexec_mach_type, machine_arch_type);
> + set(kexec_boot_atags, image->arch.kernel_r2);
We could simplify this slightly if we moved the kexec_& variables into a
struct (using asm-offset KEXEC_VAR_* offsets and a KEXEC_VAR_SIZE region
reserved in the asm), then here we could do something like:
static struct kexec_vars *kexec_buffer_vars(void *buffer)
{
unsigned long code = ((unisigned long)relocate_new_kernel) & ~1;
unsigned long vars - (unsigned long)relocate_vars;
unsigned long offset = vars - code;
return buffer + offset;
}
... and in machine_kexec() do:
struct kexec_vars *kv = kexec_buffer_vars(reboot_code_buffer);
kv->start_address = image->start;
kv->indirection_page = page_list;
kv->mach_type = machine-arch_type;
kv->boot_atags = arch.kernel_r2;
... if that looks any better to you?
Mark.
