ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 160 insertions, 0 deletions

diff --git a/arch/arm/mm/idmap.c b/arch/arm/mm/idmap.c
new file mode 100644
index 000000000..70403e968
--- /dev/null
+++ b/arch/arm/mm/idmap.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/mm_types.h>
+#include <linux/pgtable.h>
+
+#include <asm/cputype.h>
+#include <asm/idmap.h>
+#include <asm/hwcap.h>
+#include <asm/pgalloc.h>
+#include <asm/sections.h>
+#include <asm/system_info.h>
+#include <asm/uaccess.h>
+
+/*
+ * Note: accesses outside of the kernel image and the identity map area
+ * are not supported on any CPU using the idmap tables as its current
+ * page tables.
+ */
+pgd_t *idmap_pgd __ro_after_init;
+long long arch_phys_to_idmap_offset __ro_after_init;
+
+#ifdef CONFIG_ARM_LPAE
+static void idmap_add_pmd(pud_t *pud, unsigned long addr, unsigned long end,
+	unsigned long prot)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	if (pud_none_or_clear_bad(pud) || (pud_val(*pud) & L_PGD_SWAPPER)) {
+		pmd = pmd_alloc_one(&init_mm, addr);
+		if (!pmd) {
+			pr_warn("Failed to allocate identity pmd.\n");
+			return;
+		}
+		/*
+		 * Copy the original PMD to ensure that the PMD entries for
+		 * the kernel image are preserved.
+		 */
+		if (!pud_none(*pud))
+			memcpy(pmd, pmd_offset(pud, 0),
+			       PTRS_PER_PMD * sizeof(pmd_t));
+		pud_populate(&init_mm, pud, pmd);
+		pmd += pmd_index(addr);
+	} else
+		pmd = pmd_offset(pud, addr);
+
+	do {
+		next = pmd_addr_end(addr, end);
+		*pmd = __pmd((addr & PMD_MASK) | prot);
+		flush_pmd_entry(pmd);
+	} while (pmd++, addr = next, addr != end);
+}
+#else	/* !CONFIG_ARM_LPAE */
+static void idmap_add_pmd(pud_t *pud, unsigned long addr, unsigned long end,
+	unsigned long prot)
+{
+	pmd_t *pmd = pmd_offset(pud, addr);
+
+	addr = (addr & PMD_MASK) | prot;
+	pmd[0] = __pmd(addr);
+	addr += SECTION_SIZE;
+	pmd[1] = __pmd(addr);
+	flush_pmd_entry(pmd);
+}
+#endif	/* CONFIG_ARM_LPAE */
+
+static void idmap_add_pud(pgd_t *pgd, unsigned long addr, unsigned long end,
+	unsigned long prot)
+{
+	p4d_t *p4d = p4d_offset(pgd, addr);
+	pud_t *pud = pud_offset(p4d, addr);
+	unsigned long next;
+
+	do {
+		next = pud_addr_end(addr, end);
+		idmap_add_pmd(pud, addr, next, prot);
+	} while (pud++, addr = next, addr != end);
+}
+
+static void identity_mapping_add(pgd_t *pgd, const char *text_start,
+				 const char *text_end, unsigned long prot)
+{
+	unsigned long addr, end;
+	unsigned long next;
+
+#ifdef CONFIG_XIP_KERNEL
+	addr = (phys_addr_t)(text_start) - XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
+		+ CONFIG_XIP_PHYS_ADDR;
+	end = (phys_addr_t)(text_end) - XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
+		+ CONFIG_XIP_PHYS_ADDR;
+#else
+	addr = virt_to_idmap(text_start);
+	end = virt_to_idmap(text_end);
+#endif
+	pr_info("Setting up static identity map for 0x%lx - 0x%lx\n", addr, end);
+
+	prot |= PMD_TYPE_SECT | PMD_SECT_AP_WRITE | PMD_SECT_AF;
+
+	if (cpu_architecture() <= CPU_ARCH_ARMv5TEJ && !cpu_is_xscale_family())
+		prot |= PMD_BIT4;
+
+	pgd += pgd_index(addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		idmap_add_pud(pgd, addr, next, prot);
+	} while (pgd++, addr = next, addr != end);
+}
+
+extern char  __idmap_text_start[], __idmap_text_end[];
+
+static int __init init_static_idmap(void)
+{
+	idmap_pgd = pgd_alloc(&init_mm);
+	if (!idmap_pgd)
+		return -ENOMEM;
+
+	identity_mapping_add(idmap_pgd, __idmap_text_start,
+			     __idmap_text_end, 0);
+
+	/* Flush L1 for the hardware to see this page table content */
+	if (!(elf_hwcap & HWCAP_LPAE))
+		flush_cache_louis();
+
+	return 0;
+}
+early_initcall(init_static_idmap);
+
+/*
+ * In order to soft-boot, we need to switch to a 1:1 mapping for the
+ * cpu_reset functions. This will then ensure that we have predictable
+ * results when turning off the mmu.
+ */
+void setup_mm_for_reboot(void)
+{
+	/*
+	 * With CONFIG_CPU_TTBR0_PAN enabled, TTBCR.EPD0 is set whenever
+	 * user-space access is disabled in order to block TTBR0 page-table
+	 * walks.  The identity mapping lives at low (user-space) virtual
+	 * addresses and can only be reached via TTBR0, so we must re-enable
+	 * those walks before switching page tables.  On non-PAN kernels this
+	 * is a no-op.
+	 */
+	if (IS_ENABLED(CONFIG_CPU_TTBR0_PAN))
+		uaccess_save_and_enable();
+
+	/* Switch to the identity mapping. */
+	cpu_switch_mm(idmap_pgd, &init_mm);
+	local_flush_bp_all();
+
+#ifdef CONFIG_CPU_HAS_ASID
+	/*
+	 * We don't have a clean ASID for the identity mapping, which
+	 * may clash with virtual addresses of the previous page tables
+	 * and therefore potentially in the TLB.
+	 */
+	local_flush_tlb_all();
+#endif
+}