x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 491 insertions, 0 deletions

diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
new file mode 100644
index 000000000..06e6b4952
--- /dev/null
+++ b/arch/sh/mm/fault.c
@@ -0,0 +1,491 @@
+/*
+ * Page fault handler for SH with an MMU.
+ *
+ *  Copyright (C) 1999  Niibe Yutaka
+ *  Copyright (C) 2003 - 2012  Paul Mundt
+ *
+ *  Based on linux/arch/i386/mm/fault.c:
+ *   Copyright (C) 1995  Linus Torvalds
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/hardirq.h>
+#include <linux/kprobes.h>
+#include <linux/perf_event.h>
+#include <linux/kdebug.h>
+#include <linux/uaccess.h>
+#include <asm/io_trapped.h>
+#include <asm/mmu_context.h>
+#include <asm/tlbflush.h>
+#include <asm/traps.h>
+
+static void
+force_sig_info_fault(int si_signo, int si_code, unsigned long address)
+{
+	force_sig_fault(si_signo, si_code, (void __user *)address);
+}
+
+/*
+ * This is useful to dump out the page tables associated with
+ * 'addr' in mm 'mm'.
+ */
+static void show_pte(struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *pgd;
+
+	if (mm) {
+		pgd = mm->pgd;
+	} else {
+		pgd = get_TTB();
+
+		if (unlikely(!pgd))
+			pgd = swapper_pg_dir;
+	}
+
+	pr_alert("pgd = %p\n", pgd);
+	pgd += pgd_index(addr);
+	pr_alert("[%08lx] *pgd=%0*llx", addr, (u32)(sizeof(*pgd) * 2),
+		 (u64)pgd_val(*pgd));
+
+	do {
+		p4d_t *p4d;
+		pud_t *pud;
+		pmd_t *pmd;
+		pte_t *pte;
+
+		if (pgd_none(*pgd))
+			break;
+
+		if (pgd_bad(*pgd)) {
+			pr_cont("(bad)");
+			break;
+		}
+
+		p4d = p4d_offset(pgd, addr);
+		if (PTRS_PER_P4D != 1)
+			pr_cont(", *p4d=%0*Lx", (u32)(sizeof(*p4d) * 2),
+			        (u64)p4d_val(*p4d));
+
+		if (p4d_none(*p4d))
+			break;
+
+		if (p4d_bad(*p4d)) {
+			pr_cont("(bad)");
+			break;
+		}
+
+		pud = pud_offset(p4d, addr);
+		if (PTRS_PER_PUD != 1)
+			pr_cont(", *pud=%0*llx", (u32)(sizeof(*pud) * 2),
+				(u64)pud_val(*pud));
+
+		if (pud_none(*pud))
+			break;
+
+		if (pud_bad(*pud)) {
+			pr_cont("(bad)");
+			break;
+		}
+
+		pmd = pmd_offset(pud, addr);
+		if (PTRS_PER_PMD != 1)
+			pr_cont(", *pmd=%0*llx", (u32)(sizeof(*pmd) * 2),
+				(u64)pmd_val(*pmd));
+
+		if (pmd_none(*pmd))
+			break;
+
+		if (pmd_bad(*pmd)) {
+			pr_cont("(bad)");
+			break;
+		}
+
+		/* We must not map this if we have highmem enabled */
+		if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
+			break;
+
+		pte = pte_offset_kernel(pmd, addr);
+		pr_cont(", *pte=%0*llx", (u32)(sizeof(*pte) * 2),
+			(u64)pte_val(*pte));
+	} while (0);
+
+	pr_cont("\n");
+}
+
+static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
+{
+	unsigned index = pgd_index(address);
+	pgd_t *pgd_k;
+	p4d_t *p4d, *p4d_k;
+	pud_t *pud, *pud_k;
+	pmd_t *pmd, *pmd_k;
+
+	pgd += index;
+	pgd_k = init_mm.pgd + index;
+
+	if (!pgd_present(*pgd_k))
+		return NULL;
+
+	p4d = p4d_offset(pgd, address);
+	p4d_k = p4d_offset(pgd_k, address);
+	if (!p4d_present(*p4d_k))
+		return NULL;
+
+	pud = pud_offset(p4d, address);
+	pud_k = pud_offset(p4d_k, address);
+	if (!pud_present(*pud_k))
+		return NULL;
+
+	if (!pud_present(*pud))
+	    set_pud(pud, *pud_k);
+
+	pmd = pmd_offset(pud, address);
+	pmd_k = pmd_offset(pud_k, address);
+	if (!pmd_present(*pmd_k))
+		return NULL;
+
+	if (!pmd_present(*pmd))
+		set_pmd(pmd, *pmd_k);
+	else {
+		/*
+		 * The page tables are fully synchronised so there must
+		 * be another reason for the fault. Return NULL here to
+		 * signal that we have not taken care of the fault.
+		 */
+		BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
+		return NULL;
+	}
+
+	return pmd_k;
+}
+
+#ifdef CONFIG_SH_STORE_QUEUES
+#define __FAULT_ADDR_LIMIT	P3_ADDR_MAX
+#else
+#define __FAULT_ADDR_LIMIT	VMALLOC_END
+#endif
+
+/*
+ * Handle a fault on the vmalloc or module mapping area
+ */
+static noinline int vmalloc_fault(unsigned long address)
+{
+	pgd_t *pgd_k;
+	pmd_t *pmd_k;
+	pte_t *pte_k;
+
+	/* Make sure we are in vmalloc/module/P3 area: */
+	if (!(address >= VMALLOC_START && address < __FAULT_ADDR_LIMIT))
+		return -1;
+
+	/*
+	 * Synchronize this task's top level page-table
+	 * with the 'reference' page table.
+	 *
+	 * Do _not_ use "current" here. We might be inside
+	 * an interrupt in the middle of a task switch..
+	 */
+	pgd_k = get_TTB();
+	pmd_k = vmalloc_sync_one(pgd_k, address);
+	if (!pmd_k)
+		return -1;
+
+	pte_k = pte_offset_kernel(pmd_k, address);
+	if (!pte_present(*pte_k))
+		return -1;
+
+	return 0;
+}
+
+static void
+show_fault_oops(struct pt_regs *regs, unsigned long address)
+{
+	if (!oops_may_print())
+		return;
+
+	pr_alert("BUG: unable to handle kernel %s at %08lx\n",
+		 address < PAGE_SIZE ? "NULL pointer dereference"
+				     : "paging request",
+		 address);
+	pr_alert("PC:");
+	printk_address(regs->pc, 1);
+
+	show_pte(NULL, address);
+}
+
+static noinline void
+no_context(struct pt_regs *regs, unsigned long error_code,
+	   unsigned long address)
+{
+	/* Are we prepared to handle this kernel fault?  */
+	if (fixup_exception(regs))
+		return;
+
+	if (handle_trapped_io(regs, address))
+		return;
+
+	/*
+	 * Oops. The kernel tried to access some bad page. We'll have to
+	 * terminate things with extreme prejudice.
+	 */
+	bust_spinlocks(1);
+
+	show_fault_oops(regs, address);
+
+	die("Oops", regs, error_code);
+}
+
+static void
+__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
+		       unsigned long address, int si_code)
+{
+	/* User mode accesses just cause a SIGSEGV */
+	if (user_mode(regs)) {
+		/*
+		 * It's possible to have interrupts off here:
+		 */
+		local_irq_enable();
+
+		force_sig_info_fault(SIGSEGV, si_code, address);
+
+		return;
+	}
+
+	no_context(regs, error_code, address);
+}
+
+static noinline void
+bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
+		     unsigned long address)
+{
+	__bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR);
+}
+
+static void
+__bad_area(struct pt_regs *regs, unsigned long error_code,
+	   unsigned long address, int si_code)
+{
+	struct mm_struct *mm = current->mm;
+
+	/*
+	 * Something tried to access memory that isn't in our memory map..
+	 * Fix it, but check if it's kernel or user first..
+	 */
+	mmap_read_unlock(mm);
+
+	__bad_area_nosemaphore(regs, error_code, address, si_code);
+}
+
+static noinline void
+bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
+{
+	__bad_area(regs, error_code, address, SEGV_MAPERR);
+}
+
+static noinline void
+bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
+		      unsigned long address)
+{
+	__bad_area(regs, error_code, address, SEGV_ACCERR);
+}
+
+static void
+do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address)
+{
+	struct task_struct *tsk = current;
+	struct mm_struct *mm = tsk->mm;
+
+	mmap_read_unlock(mm);
+
+	/* Kernel mode? Handle exceptions or die: */
+	if (!user_mode(regs))
+		no_context(regs, error_code, address);
+
+	force_sig_info_fault(SIGBUS, BUS_ADRERR, address);
+}
+
+static noinline int
+mm_fault_error(struct pt_regs *regs, unsigned long error_code,
+	       unsigned long address, vm_fault_t fault)
+{
+	/*
+	 * Pagefault was interrupted by SIGKILL. We have no reason to
+	 * continue pagefault.
+	 */
+	if (fault_signal_pending(fault, regs)) {
+		if (!user_mode(regs))
+			no_context(regs, error_code, address);
+		return 1;
+	}
+
+	/* Release mmap_lock first if necessary */
+	if (!(fault & VM_FAULT_RETRY))
+		mmap_read_unlock(current->mm);
+
+	if (!(fault & VM_FAULT_ERROR))
+		return 0;
+
+	if (fault & VM_FAULT_OOM) {
+		/* Kernel mode? Handle exceptions or die: */
+		if (!user_mode(regs)) {
+			no_context(regs, error_code, address);
+			return 1;
+		}
+
+		/*
+		 * We ran out of memory, call the OOM killer, and return the
+		 * userspace (which will retry the fault, or kill us if we got
+		 * oom-killed):
+		 */
+		pagefault_out_of_memory();
+	} else {
+		if (fault & VM_FAULT_SIGBUS)
+			do_sigbus(regs, error_code, address);
+		else if (fault & VM_FAULT_SIGSEGV)
+			bad_area(regs, error_code, address);
+		else
+			BUG();
+	}
+
+	return 1;
+}
+
+static inline int access_error(int error_code, struct vm_area_struct *vma)
+{
+	if (error_code & FAULT_CODE_WRITE) {
+		/* write, present and write, not present: */
+		if (unlikely(!(vma->vm_flags & VM_WRITE)))
+			return 1;
+		return 0;
+	}
+
+	/* ITLB miss on NX page */
+	if (unlikely((error_code & FAULT_CODE_ITLB) &&
+		     !(vma->vm_flags & VM_EXEC)))
+		return 1;
+
+	/* read, not present: */
+	if (unlikely(!vma_is_accessible(vma)))
+		return 1;
+
+	return 0;
+}
+
+static int fault_in_kernel_space(unsigned long address)
+{
+	return address >= TASK_SIZE;
+}
+
+/*
+ * This routine handles page faults.  It determines the address,
+ * and the problem, and then passes it off to one of the appropriate
+ * routines.
+ */
+asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
+					unsigned long error_code,
+					unsigned long address)
+{
+	unsigned long vec;
+	struct task_struct *tsk;
+	struct mm_struct *mm;
+	struct vm_area_struct * vma;
+	vm_fault_t fault;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
+
+	tsk = current;
+	mm = tsk->mm;
+	vec = lookup_exception_vector();
+
+	/*
+	 * We fault-in kernel-space virtual memory on-demand. The
+	 * 'reference' page table is init_mm.pgd.
+	 *
+	 * NOTE! We MUST NOT take any locks for this case. We may
+	 * be in an interrupt or a critical region, and should
+	 * only copy the information from the master page table,
+	 * nothing more.
+	 */
+	if (unlikely(fault_in_kernel_space(address))) {
+		if (vmalloc_fault(address) >= 0)
+			return;
+		if (kprobe_page_fault(regs, vec))
+			return;
+
+		bad_area_nosemaphore(regs, error_code, address);
+		return;
+	}
+
+	if (unlikely(kprobe_page_fault(regs, vec)))
+		return;
+
+	/* Only enable interrupts if they were on before the fault */
+	if ((regs->sr & SR_IMASK) != SR_IMASK)
+		local_irq_enable();
+
+	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
+
+	/*
+	 * If we're in an interrupt, have no user context or are running
+	 * with pagefaults disabled then we must not take the fault:
+	 */
+	if (unlikely(faulthandler_disabled() || !mm)) {
+		bad_area_nosemaphore(regs, error_code, address);
+		return;
+	}
+
+retry:
+	vma = lock_mm_and_find_vma(mm, address, regs);
+	if (unlikely(!vma)) {
+		bad_area_nosemaphore(regs, error_code, address);
+		return;
+	}
+
+	/*
+	 * Ok, we have a good vm_area for this memory access, so
+	 * we can handle it..
+	 */
+	if (unlikely(access_error(error_code, vma))) {
+		bad_area_access_error(regs, error_code, address);
+		return;
+	}
+
+	set_thread_fault_code(error_code);
+
+	if (user_mode(regs))
+		flags |= FAULT_FLAG_USER;
+	if (error_code & FAULT_CODE_WRITE)
+		flags |= FAULT_FLAG_WRITE;
+
+	/*
+	 * If for any reason at all we couldn't handle the fault,
+	 * make sure we exit gracefully rather than endlessly redo
+	 * the fault.
+	 */
+	fault = handle_mm_fault(vma, address, flags, regs);
+
+	if (unlikely(fault & (VM_FAULT_RETRY | VM_FAULT_ERROR)))
+		if (mm_fault_error(regs, error_code, address, fault))
+			return;
+
+	/* The fault is fully completed (including releasing mmap lock) */
+	if (fault & VM_FAULT_COMPLETED)
+		return;
+
+	if (fault & VM_FAULT_RETRY) {
+		flags |= FAULT_FLAG_TRIED;
+
+		/*
+		 * No need to mmap_read_unlock(mm) as we would
+		 * have already released it in __lock_page_or_retry
+		 * in mm/filemap.c.
+		 */
+		goto retry;
+	}
+
+	mmap_read_unlock(mm);
+}