On 19 January 2018 at 06:56, Lingutla Chandrasekhar
<clingutla@xxxxxxxxxxxxxx> wrote:
> Sometime kernel image and dtb load offsets can overlap due to
> dynamically increased Image or dtb size if both load addresses
> are near to each other, which leads to bootup failures.
>
> So validate dtb load address and kernel image, if they overlap
> do not proceed to boot.
>
> Signed-off-by: Lingutla Chandrasekhar <clingutla@xxxxxxxxxxxxxx>
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 30ad2f085d1f..c9dd699f09ab 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -181,11 +181,17 @@ static void __init smp_build_mpidr_hash(void)
> static void __init setup_machine_fdt(phys_addr_t dt_phys)
> {
> void *dt_virt = fixmap_remap_fdt(dt_phys);
> + u64 end_phys = __pa_symbol(_end);
> + u64 start_phys = __pa_symbol(_text);
> const char *name;
>
> - if (!dt_virt || !early_init_dt_scan(dt_virt)) {
> + if (!dt_virt || ((dt_phys < start_phys) &&
> + ((dt_phys + fdt_totalsize(dt_virt)) > start_phys)) ||
> + ((dt_phys > start_phys) && (dt_phys < end_phys)) ||
> + !early_init_dt_scan(dt_virt)) {
> pr_crit("\n"
> "Error: invalid device tree blob at physical address %pa (virtual address 0x%p)\n"
> + "The dtb load address should not overlap with kernel image\n"
> "The dtb must be 8-byte aligned and must not exceed 2 MB in size\n"
> "\nPlease check your bootloader.",
> &dt_phys, dt_virt);
Paradoxically, this pr_crit() will only ever be able to produce
readable output if early_init_dt_scan() returns success. If not, no
early DT parsing will have occurred, and we will have no idea where
the UART is nor whether earlycon was passed via /chosen/bootargs.
That means adding the check before the call to early_init_dt_scan() is
not very helpful, since the system will just hang with no output.
If you really want to check for overlap, please do it *after* the
if(), as a separate WARN_ON() that does not force the boot to fail.
This has a much higher likelihood of anyone ever reading your error
message, and being able to do something about it.
Also, checking for overlap can be done using two comparisons:
end1 > start2 && end2 > start1
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