On Thu, 2 Jun 2022 at 23:22, Jason A. Donenfeld <[email protected]> wrote:
>
> Stephen reported that a static key warning splat appears during early
> boot on arm64 systems that credit randomness from device trees that
> contain an "rng-seed" property, because setup_machine_fdt() is called
> before jump_label_init() during setup_arch(), which was fixed by
> 73e2d827a501 ("arm64: Initialize jump labels before
> setup_machine_fdt()").
>
> Upon cursory inspection, the same basic issue appears to apply to arm32
> as well. In this case, we reorder setup_arch() to do things in the same
> order as is now the case on arm64.
>
> Reported-by: Stephen Boyd <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: Ard Biesheuvel <[email protected]>
> Cc: [email protected]
> Fixes: f5bda35fba61 ("random: use static branch for crng_ready()")
Wouldn't it be better to defer the
static_branch_enable(&crng_is_ready) call to later in the boot (e.g.,
using an initcall()), rather than going around 'fixing' fragile,
working early boot code across multiple architectures?
> Signed-off-by: Jason A. Donenfeld <[email protected]>
> ---
> arch/arm/kernel/setup.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 1e8a50a97edf..ef40d9f5d5a7 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -1097,10 +1097,15 @@ void __init setup_arch(char **cmdline_p)
> const struct machine_desc *mdesc = NULL;
> void *atags_vaddr = NULL;
>
> + setup_initial_init_mm(_text, _etext, _edata, _end);
> + setup_processor();
> + early_fixmap_init();
> + early_ioremap_init();
> + jump_label_init();
> +
Is it really necessary to reorder all these calls? What does
jump_label_init() actually need?
If this is related to the code patching, I wonder whether it wouldn't
be better not to rewrite all the NOPs (this is a x86-ism as every new
x86 uarch appears to have a better [faster?] NOP than the previous
one)
The issue with changes like these is that we might end up with bug
report in ~3 months' time that 'obscure platform X no longer boots or
produces any output'. In the best case, we'll have a bisect report
identifying this patch, but we won't be able to simply revert it as it
would reintroduce this issue into a kernel that is now stable.
> if (__atags_pointer)
> atags_vaddr = FDT_VIRT_BASE(__atags_pointer);
>
> - setup_processor();
> if (atags_vaddr) {
> mdesc = setup_machine_fdt(atags_vaddr);
> if (mdesc)
> @@ -1125,15 +1130,10 @@ void __init setup_arch(char **cmdline_p)
> if (mdesc->reboot_mode != REBOOT_HARD)
> reboot_mode = mdesc->reboot_mode;
>
> - setup_initial_init_mm(_text, _etext, _edata, _end);
> -
> /* populate cmd_line too for later use, preserving boot_command_line */
> strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
> *cmdline_p = cmd_line;
>
> - early_fixmap_init();
> - early_ioremap_init();
> -
> parse_early_param();
>
> #ifdef CONFIG_MMU
> --
> 2.35.1
>