On Mon, Oct 20, 2025 at 5:08 PM Pasha Tatashin
<[email protected]> wrote:
>
> It is invalid for KHO metadata or preserved memory regions to be located
> within the KHO scratch area, as this area is overwritten when the next
> kernel is loaded, and used early in boot by the next kernel. This can
> lead to memory corruption.
>
> Adds checks to kho_preserve_* and KHO's internal metadata allocators
> (xa_load_or_alloc, new_chunk) to verify that the physical address of the
> memory does not overlap with any defined scratch region. If an overlap
> is detected, the operation will fail and a WARN_ON is triggered. To
> avoid performance overhead in production kernels, these checks are
> enabled only when CONFIG_KEXEC_HANDOVER_DEBUG is selected.
How many scratch regions are there in practice? Checking
unconditionally seems like a small price to pay to avoid possible
memory corruption. Especially since most KHO preservation should
happen while the VM is still running (so does not have to by
hyper-optimized).
> static void *xa_load_or_alloc(struct xarray *xa, unsigned long index, size_t
> sz)
> {
> - void *elm, *res;
> + void *res = xa_load(xa, index);
>
> - elm = xa_load(xa, index);
> - if (elm)
> - return elm;
> + if (res)
> + return res;
> +
> + void *elm __free(kfree) = kzalloc(sz, GFP_KERNEL);
nit: This breaks the local style of always declaring variables at the
beginning of blocks.
