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, 306 insertions, 0 deletions

diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
new file mode 100644
index 000000000..e1f5e9abb
--- /dev/null
+++ b/drivers/misc/lkdtm/perms.c
@@ -0,0 +1,306 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This is for all the tests related to validating kernel memory
+ * permissions: non-executable regions, non-writable regions, and
+ * even non-readable regions.
+ */
+#include "lkdtm.h"
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/mman.h>
+#include <linux/uaccess.h>
+#include <linux/objtool.h>
+#include <asm/cacheflush.h>
+#include <asm/sections.h>
+
+/* Whether or not to fill the target memory area with do_nothing(). */
+#define CODE_WRITE	true
+#define CODE_AS_IS	false
+
+/* How many bytes to copy to be sure we've copied enough of do_nothing(). */
+#define EXEC_SIZE 64
+
+/* This is non-const, so it will end up in the .data section. */
+static u8 data_area[EXEC_SIZE];
+
+/* This is const, so it will end up in the .rodata section. */
+static const unsigned long rodata = 0xAA55AA55;
+
+/* This is marked __ro_after_init, so it should ultimately be .rodata. */
+static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
+
+/*
+ * This is a pointer to do_nothing() which is initialized at runtime rather
+ * than build time to avoid objtool IBT validation warnings caused by an
+ * inlined unrolled memcpy() in execute_location().
+ */
+static void __ro_after_init *do_nothing_ptr;
+
+/*
+ * This just returns to the caller. It is designed to be copied into
+ * non-executable memory regions.
+ */
+static noinline void do_nothing(void)
+{
+	return;
+}
+
+/* Must immediately follow do_nothing for size calculuations to work out. */
+static noinline void do_overwritten(void)
+{
+	pr_info("do_overwritten wasn't overwritten!\n");
+	return;
+}
+
+static noinline void do_almost_nothing(void)
+{
+	pr_info("do_nothing was hijacked!\n");
+}
+
+static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)
+{
+	if (!have_function_descriptors())
+		return dst;
+
+	memcpy(fdesc, do_nothing, sizeof(*fdesc));
+	fdesc->addr = (unsigned long)dst;
+	barrier();
+
+	return fdesc;
+}
+
+static noinline __nocfi void execute_location(void *dst, bool write)
+{
+	void (*func)(void);
+	func_desc_t fdesc;
+
+	pr_info("attempting ok execution at %px\n", do_nothing_ptr);
+	do_nothing();
+
+	if (write == CODE_WRITE) {
+		memcpy(dst, do_nothing_ptr, EXEC_SIZE);
+		flush_icache_range((unsigned long)dst,
+				   (unsigned long)dst + EXEC_SIZE);
+	}
+	pr_info("attempting bad execution at %px\n", dst);
+	func = setup_function_descriptor(&fdesc, dst);
+	func();
+	pr_err("FAIL: func returned\n");
+}
+/*
+ * Explicitly doing the wrong thing for testing.
+ */
+ANNOTATE_NOCFI_SYM(execute_location);
+
+static void execute_user_location(void *dst)
+{
+	int copied;
+
+	/* Intentionally crossing kernel/user memory boundary. */
+	void (*func)(void);
+	func_desc_t fdesc;
+	void *do_nothing_text = dereference_function_descriptor(do_nothing);
+
+	pr_info("attempting ok execution at %px\n", do_nothing_text);
+	do_nothing();
+
+	copied = access_process_vm(current, (unsigned long)dst, do_nothing_text,
+				   EXEC_SIZE, FOLL_WRITE);
+	if (copied < EXEC_SIZE)
+		return;
+	pr_info("attempting bad execution at %px\n", dst);
+	func = setup_function_descriptor(&fdesc, dst);
+	func();
+	pr_err("FAIL: func returned\n");
+}
+
+static void lkdtm_WRITE_RO(void)
+{
+	/* Explicitly cast away "const" for the test and make volatile. */
+	volatile unsigned long *ptr = (unsigned long *)&rodata;
+
+	pr_info("attempting bad rodata write at %px\n", ptr);
+	*ptr ^= 0xabcd1234;
+	pr_err("FAIL: survived bad write\n");
+}
+
+static void lkdtm_WRITE_RO_AFTER_INIT(void)
+{
+	volatile unsigned long *ptr = &ro_after_init;
+
+	/*
+	 * Verify we were written to during init. Since an Oops
+	 * is considered a "success", a failure is to just skip the
+	 * real test.
+	 */
+	if ((*ptr & 0xAA) != 0xAA) {
+		pr_info("%p was NOT written during init!?\n", ptr);
+		return;
+	}
+
+	pr_info("attempting bad ro_after_init write at %px\n", ptr);
+	*ptr ^= 0xabcd1234;
+	pr_err("FAIL: survived bad write\n");
+}
+
+static void lkdtm_WRITE_KERN(void)
+{
+	size_t size;
+	volatile unsigned char *ptr;
+
+	size = (unsigned long)dereference_function_descriptor(do_overwritten) -
+	       (unsigned long)dereference_function_descriptor(do_nothing);
+	ptr = dereference_function_descriptor(do_overwritten);
+
+	pr_info("attempting bad %zu byte write at %px\n", size, ptr);
+	memcpy((void *)ptr, (unsigned char *)do_nothing, size);
+	flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size));
+	pr_err("FAIL: survived bad write\n");
+
+	do_overwritten();
+}
+
+static void lkdtm_WRITE_OPD(void)
+{
+	size_t size = sizeof(func_desc_t);
+	void (*func)(void) = do_nothing;
+
+	if (!have_function_descriptors()) {
+		pr_info("XFAIL: Platform doesn't use function descriptors.\n");
+		return;
+	}
+	pr_info("attempting bad %zu bytes write at %px\n", size, do_nothing);
+	memcpy(do_nothing, do_almost_nothing, size);
+	pr_err("FAIL: survived bad write\n");
+
+	asm("" : "=m"(func));
+	func();
+}
+
+static void lkdtm_EXEC_DATA(void)
+{
+	execute_location(data_area, CODE_WRITE);
+}
+
+static void lkdtm_EXEC_STACK(void)
+{
+	u8 stack_area[EXEC_SIZE];
+	execute_location(stack_area, CODE_WRITE);
+}
+
+static void lkdtm_EXEC_KMALLOC(void)
+{
+	u32 *kmalloc_area = kmalloc(EXEC_SIZE, GFP_KERNEL);
+	execute_location(kmalloc_area, CODE_WRITE);
+	kfree(kmalloc_area);
+}
+
+static void lkdtm_EXEC_VMALLOC(void)
+{
+	u32 *vmalloc_area = vmalloc(EXEC_SIZE);
+	execute_location(vmalloc_area, CODE_WRITE);
+	vfree(vmalloc_area);
+}
+
+static void lkdtm_EXEC_RODATA(void)
+{
+	execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing),
+			 CODE_AS_IS);
+}
+
+static void lkdtm_EXEC_USERSPACE(void)
+{
+	unsigned long user_addr;
+
+	user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
+			    PROT_READ | PROT_WRITE | PROT_EXEC,
+			    MAP_ANONYMOUS | MAP_PRIVATE, 0);
+	if (user_addr >= TASK_SIZE) {
+		pr_warn("Failed to allocate user memory\n");
+		return;
+	}
+	execute_user_location((void *)user_addr);
+	vm_munmap(user_addr, PAGE_SIZE);
+}
+
+static void lkdtm_EXEC_NULL(void)
+{
+	execute_location(NULL, CODE_AS_IS);
+}
+
+static void lkdtm_ACCESS_USERSPACE(void)
+{
+	unsigned long user_addr, tmp = 0;
+	unsigned long *ptr;
+
+	user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
+			    PROT_READ | PROT_WRITE | PROT_EXEC,
+			    MAP_ANONYMOUS | MAP_PRIVATE, 0);
+	if (user_addr >= TASK_SIZE) {
+		pr_warn("Failed to allocate user memory\n");
+		return;
+	}
+
+	if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) {
+		pr_warn("copy_to_user failed\n");
+		vm_munmap(user_addr, PAGE_SIZE);
+		return;
+	}
+
+	ptr = (unsigned long *)user_addr;
+
+	pr_info("attempting bad read at %px\n", ptr);
+	tmp = *ptr;
+	tmp += 0xc0dec0de;
+	pr_err("FAIL: survived bad read\n");
+
+	pr_info("attempting bad write at %px\n", ptr);
+	*ptr = tmp;
+	pr_err("FAIL: survived bad write\n");
+
+	vm_munmap(user_addr, PAGE_SIZE);
+}
+
+static void lkdtm_ACCESS_NULL(void)
+{
+	unsigned long tmp;
+	volatile unsigned long *ptr = (unsigned long *)NULL;
+
+	pr_info("attempting bad read at %px\n", ptr);
+	tmp = *ptr;
+	tmp += 0xc0dec0de;
+	pr_err("FAIL: survived bad read\n");
+
+	pr_info("attempting bad write at %px\n", ptr);
+	*ptr = tmp;
+	pr_err("FAIL: survived bad write\n");
+}
+
+void __init lkdtm_perms_init(void)
+{
+	do_nothing_ptr = dereference_function_descriptor(do_nothing);
+
+	/* Make sure we can write to __ro_after_init values during __init */
+	ro_after_init |= 0xAA;
+}
+
+static struct crashtype crashtypes[] = {
+	CRASHTYPE(WRITE_RO),
+	CRASHTYPE(WRITE_RO_AFTER_INIT),
+	CRASHTYPE(WRITE_KERN),
+	CRASHTYPE(WRITE_OPD),
+	CRASHTYPE(EXEC_DATA),
+	CRASHTYPE(EXEC_STACK),
+	CRASHTYPE(EXEC_KMALLOC),
+	CRASHTYPE(EXEC_VMALLOC),
+	CRASHTYPE(EXEC_RODATA),
+	CRASHTYPE(EXEC_USERSPACE),
+	CRASHTYPE(EXEC_NULL),
+	CRASHTYPE(ACCESS_USERSPACE),
+	CRASHTYPE(ACCESS_NULL),
+};
+
+struct crashtype_category perms_crashtypes = {
+	.crashtypes = crashtypes,
+	.len	    = ARRAY_SIZE(crashtypes),
+};