linux-kernel - [PATCH v3] ARM: initialize jump labels before setup_machine

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Message-Id: <20220607193044.1063287-1-Jason@zx2c4.com>
Date:   Tue,  7 Jun 2022 21:30:44 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Phil Elwell <phil@...pberrypi.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Russel King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>
Subject: [PATCH v3] ARM: initialize jump labels before setup_machine_fdt()

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()").

The same basic issue applies to arm32 as well. So this commit adds a
call to jump_label_init() just before setup_machine_fdt(). Since the
page maps haven't been set yet, this also requires us to use the early
patching code in the jump label code.

Reported-by: Stephen Boyd <swboyd@...omium.org>
Reported-by: Phil Elwell <phil@...pberrypi.com>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: Russel King <linux@...linux.org.uk>
Cc: Catalin Marinas <catalin.marinas@....com>
Fixes: f5bda35fba61 ("random: use static branch for crng_ready()")
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 arch/arm/kernel/jump_label.c | 3 ++-
 arch/arm/kernel/setup.c      | 1 +
 arch/arm/mm/mmu.c            | 3 +++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
index 303b3ab87f7e..8f8c5312f917 100644
--- a/arch/arm/kernel/jump_label.c
+++ b/arch/arm/kernel/jump_label.c
@@ -8,6 +8,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
 					enum jump_label_type type,
 					bool is_static)
 {
+	extern bool early_mm_initialized;
 	void *addr = (void *)entry->code;
 	unsigned int insn;
 
@@ -16,7 +17,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
 	else
 		insn = arm_gen_nop();
 
-	if (is_static)
+	if (is_static || !early_mm_initialized)
 		__patch_text_early(addr, insn);
 	else
 		patch_text(addr, insn);
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 1e8a50a97edf..3ff80b1ee0b5 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -1101,6 +1101,7 @@ void __init setup_arch(char **cmdline_p)
 		atags_vaddr = FDT_VIRT_BASE(__atags_pointer);
 
 	setup_processor();
+	jump_label_init();
 	if (atags_vaddr) {
 		mdesc = setup_machine_fdt(atags_vaddr);
 		if (mdesc)
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 5e2be37a198e..3f63a5581966 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1754,10 +1754,13 @@ void __init paging_init(const struct machine_desc *mdesc)
 	__flush_dcache_page(NULL, empty_zero_page);
 }
 
+bool early_mm_initialized;
+
 void __init early_mm_init(const struct machine_desc *mdesc)
 {
 	build_mem_type_table();
 	early_paging_init(mdesc);
+	early_mm_initialized = true;
 }
 
 void set_pte_at(struct mm_struct *mm, unsigned long addr,
-- 
2.35.1