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, 190 insertions, 0 deletions

diff --git a/arch/alpha/boot/main.c b/arch/alpha/boot/main.c
new file mode 100644
index 000000000..22a1cb026
--- /dev/null
+++ b/arch/alpha/boot/main.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * arch/alpha/boot/main.c
+ *
+ * Copyright (C) 1994, 1995 Linus Torvalds
+ *
+ * This file is the bootloader for the Linux/AXP kernel
+ */
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <generated/utsrelease.h>
+#include <linux/mm.h>
+
+#include <asm/console.h>
+#include <asm/hwrpb.h>
+
+#include <linux/stdarg.h>
+
+#include "ksize.h"
+
+extern unsigned long switch_to_osf_pal(unsigned long nr,
+	struct pcb_struct * pcb_va, struct pcb_struct * pcb_pa,
+	unsigned long *vptb);
+struct hwrpb_struct *hwrpb = INIT_HWRPB;
+static struct pcb_struct pcb_va[1];
+
+/*
+ * Find a physical address of a virtual object..
+ *
+ * This is easy using the virtual page table address.
+ */
+
+static inline void *
+find_pa(unsigned long *vptb, void *ptr)
+{
+	unsigned long address = (unsigned long) ptr;
+	unsigned long result;
+
+	result = vptb[address >> 13];
+	result >>= 32;
+	result <<= 13;
+	result |= address & 0x1fff;
+	return (void *) result;
+}	
+
+/*
+ * This function moves into OSF/1 pal-code, and has a temporary
+ * PCB for that. The kernel proper should replace this PCB with
+ * the real one as soon as possible.
+ *
+ * The page table muckery in here depends on the fact that the boot
+ * code has the L1 page table identity-map itself in the second PTE
+ * in the L1 page table. Thus the L1-page is virtually addressable
+ * itself (through three levels) at virtual address 0x200802000.
+ */
+
+#define VPTB	((unsigned long *) 0x200000000)
+#define L1	((unsigned long *) 0x200802000)
+
+void
+pal_init(void)
+{
+	unsigned long i, rev;
+	struct percpu_struct * percpu;
+	struct pcb_struct * pcb_pa;
+
+	/* Create the dummy PCB.  */
+	pcb_va->ksp = 0;
+	pcb_va->usp = 0;
+	pcb_va->ptbr = L1[1] >> 32;
+	pcb_va->asn = 0;
+	pcb_va->pcc = 0;
+	pcb_va->unique = 0;
+	pcb_va->flags = 1;
+	pcb_va->res1 = 0;
+	pcb_va->res2 = 0;
+	pcb_pa = find_pa(VPTB, pcb_va);
+
+	/*
+	 * a0 = 2 (OSF)
+	 * a1 = return address, but we give the asm the vaddr of the PCB
+	 * a2 = physical addr of PCB
+	 * a3 = new virtual page table pointer
+	 * a4 = KSP (but the asm sets it)
+	 */
+	srm_printk("Switching to OSF PAL-code .. ");
+
+	i = switch_to_osf_pal(2, pcb_va, pcb_pa, VPTB);
+	if (i) {
+		srm_printk("failed, code %ld\n", i);
+		__halt();
+	}
+
+	percpu = (struct percpu_struct *)
+		(INIT_HWRPB->processor_offset + (unsigned long) INIT_HWRPB);
+	rev = percpu->pal_revision = percpu->palcode_avail[2];
+
+	srm_printk("Ok (rev %lx)\n", rev);
+
+	tbia(); /* do it directly in case we are SMP */
+}
+
+static inline long openboot(void)
+{
+	char bootdev[256];
+	long result;
+
+	result = callback_getenv(ENV_BOOTED_DEV, bootdev, 255);
+	if (result < 0)
+		return result;
+	return callback_open(bootdev, result & 255);
+}
+
+static inline long close(long dev)
+{
+	return callback_close(dev);
+}
+
+static inline long load(long dev, unsigned long addr, unsigned long count)
+{
+	char bootfile[256];
+	extern char _end;
+	long result, boot_size = &_end - (char *) BOOT_ADDR;
+
+	result = callback_getenv(ENV_BOOTED_FILE, bootfile, 255);
+	if (result < 0)
+		return result;
+	result &= 255;
+	bootfile[result] = '\0';
+	if (result)
+		srm_printk("Boot file specification (%s) not implemented\n",
+		       bootfile);
+	return callback_read(dev, count, (void *)addr, boot_size/512 + 1);
+}
+
+/*
+ * Start the kernel.
+ */
+static void runkernel(void)
+{
+	__asm__ __volatile__(
+		"bis %1,%1,$30\n\t"
+		"bis %0,%0,$26\n\t"
+		"ret ($26)"
+		: /* no outputs: it doesn't even return */
+		: "r" (START_ADDR),
+		  "r" (PAGE_SIZE + INIT_STACK));
+}
+
+void start_kernel(void)
+{
+	long i;
+	long dev;
+	int nbytes;
+	char envval[256];
+
+	srm_printk("Linux/AXP bootloader for Linux " UTS_RELEASE "\n");
+	if (INIT_HWRPB->pagesize != 8192) {
+		srm_printk("Expected 8kB pages, got %ldkB\n", INIT_HWRPB->pagesize >> 10);
+		return;
+	}
+	pal_init();
+	dev = openboot();
+	if (dev < 0) {
+		srm_printk("Unable to open boot device: %016lx\n", dev);
+		return;
+	}
+	dev &= 0xffffffff;
+	srm_printk("Loading vmlinux ...");
+	i = load(dev, START_ADDR, KERNEL_SIZE);
+	close(dev);
+	if (i != KERNEL_SIZE) {
+		srm_printk("Failed (%lx)\n", i);
+		return;
+	}
+
+	nbytes = callback_getenv(ENV_BOOTED_OSFLAGS, envval, sizeof(envval));
+	if (nbytes < 0) {
+		nbytes = 0;
+	}
+	envval[nbytes] = '\0';
+	strcpy((char*)ZERO_PGE, envval);
+
+	srm_printk(" Ok\nNow booting the kernel\n");
+	runkernel();
+	for (i = 0 ; i < 0x100000000 ; i++)
+		/* nothing */;
+	__halt();
+}