Re: [PATCH] ARM: initialize jump labels before setup_machine_fdt()

On Thu, 2 Jun 2022 at 23:22, Jason A. Donenfeld Jason@zx2c4.com 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 swboyd@chromium.org Cc: Catalin Marinas catalin.marinas@arm.com Cc: Ard Biesheuvel ardb@kernel.org Cc: stable@vger.kernel.org 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 Jason@zx2c4.com

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