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, 257 insertions, 0 deletions

diff --git a/drivers/scsi/scsicam.c b/drivers/scsi/scsicam.c
new file mode 100644
index 000000000..887de505b
--- /dev/null
+++ b/drivers/scsi/scsicam.c
@@ -0,0 +1,257 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc.
+ *
+ * Copyright 1993, 1994 Drew Eckhardt
+ *      Visionary Computing 
+ *      (Unix and Linux consulting and custom programming)
+ *      drew@Colorado.EDU
+ *      +1 (303) 786-7975
+ *
+ * For more information, please consult the SCSI-CAM draft.
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/blkdev.h>
+#include <linux/pagemap.h>
+#include <linux/msdos_partition.h>
+#include <linux/unaligned.h>
+
+#include <scsi/scsicam.h>
+
+/**
+ * scsi_bios_ptable - Read PC partition table out of first sector of device.
+ * @dev: from this device
+ *
+ * Description: Reads the first sector from the device and returns %0x42 bytes
+ *              starting at offset %0x1be.
+ * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error.
+ */
+unsigned char *scsi_bios_ptable(struct gendisk *dev)
+{
+	struct address_space *mapping = dev->part0->bd_mapping;
+	unsigned char *res = NULL;
+	struct folio *folio;
+
+	folio = read_mapping_folio(mapping, 0, NULL);
+	if (IS_ERR(folio))
+		return NULL;
+
+	res = kmemdup(folio_address(folio) + 0x1be, 66, GFP_KERNEL);
+	folio_put(folio);
+	return res;
+}
+EXPORT_SYMBOL(scsi_bios_ptable);
+
+/**
+ * scsi_partsize - Parse cylinders/heads/sectors from PC partition table
+ * @disk: gendisk of the disk to parse
+ * @capacity: size of the disk in sectors
+ * @geom: output in form of [hds, cylinders, sectors]
+ *
+ * Determine the BIOS mapping/geometry used to create the partition
+ * table, storing the results in @geom.
+ *
+ * Returns: %false on failure, %true on success.
+ */
+bool scsi_partsize(struct gendisk *disk, sector_t capacity, int geom[3])
+{
+	int cyl, ext_cyl, end_head, end_cyl, end_sector;
+	unsigned int logical_end, physical_end, ext_physical_end;
+	struct msdos_partition *p, *largest = NULL;
+	void *buf;
+	int ret = false;
+
+	buf = scsi_bios_ptable(disk);
+	if (!buf)
+		return false;
+
+	if (*(unsigned short *) (buf + 64) == 0xAA55) {
+		int largest_cyl = -1, i;
+
+		for (i = 0, p = buf; i < 4; i++, p++) {
+			if (!p->sys_ind)
+				continue;
+#ifdef DEBUG
+			printk("scsicam_bios_param : partition %d has system \n",
+			       i);
+#endif
+			cyl = p->cyl + ((p->sector & 0xc0) << 2);
+			if (cyl > largest_cyl) {
+				largest_cyl = cyl;
+				largest = p;
+			}
+		}
+	}
+	if (largest) {
+		end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);
+		end_head = largest->end_head;
+		end_sector = largest->end_sector & 0x3f;
+
+		if (end_head + 1 == 0 || end_sector == 0)
+			goto out_free_buf;
+
+#ifdef DEBUG
+		printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
+		       end_head, end_cyl, end_sector);
+#endif
+
+		physical_end = end_cyl * (end_head + 1) * end_sector +
+		    end_head * end_sector + end_sector;
+
+		/* This is the actual _sector_ number at the end */
+		logical_end = get_unaligned_le32(&largest->start_sect)
+		    + get_unaligned_le32(&largest->nr_sects);
+
+		/* This is for >1023 cylinders */
+		ext_cyl = (logical_end - (end_head * end_sector + end_sector))
+		    / (end_head + 1) / end_sector;
+		ext_physical_end = ext_cyl * (end_head + 1) * end_sector +
+		    end_head * end_sector + end_sector;
+
+#ifdef DEBUG
+		printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n"
+		  ,logical_end, physical_end, ext_physical_end, ext_cyl);
+#endif
+
+		if (logical_end == physical_end ||
+		    (end_cyl == 1023 && ext_physical_end == logical_end)) {
+			geom[0] = end_head + 1;
+			geom[1] = end_sector;
+			geom[2] = (unsigned long)capacity /
+				((end_head + 1) * end_sector);
+			ret = true;
+			goto out_free_buf;
+		}
+#ifdef DEBUG
+		printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
+		       logical_end, physical_end);
+#endif
+	}
+
+out_free_buf:
+	kfree(buf);
+	return ret;
+}
+EXPORT_SYMBOL(scsi_partsize);
+
+/*
+ * Function : static int setsize(unsigned long capacity,unsigned int *cyls,
+ *      unsigned int *hds, unsigned int *secs);
+ *
+ * Purpose : to determine a near-optimal int 0x13 mapping for a
+ *      SCSI disk in terms of lost space of size capacity, storing
+ *      the results in *cyls, *hds, and *secs.
+ *
+ * Returns : -1 on failure, 0 on success.
+ *
+ * Extracted from
+ *
+ * WORKING                                                    X3T9.2
+ * DRAFT                                                        792D
+ * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
+ *
+ *                                                        Revision 6
+ *                                                         10-MAR-94
+ * Information technology -
+ * SCSI-2 Common access method
+ * transport and SCSI interface module
+ * 
+ * ANNEX A :
+ *
+ * setsize() converts a read capacity value to int 13h
+ * head-cylinder-sector requirements. It minimizes the value for
+ * number of heads and maximizes the number of cylinders. This
+ * will support rather large disks before the number of heads
+ * will not fit in 4 bits (or 6 bits). This algorithm also
+ * minimizes the number of sectors that will be unused at the end
+ * of the disk while allowing for very large disks to be
+ * accommodated. This algorithm does not use physical geometry. 
+ */
+
+static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
+		   unsigned int *secs)
+{
+	unsigned int rv = 0;
+	unsigned long heads, sectors, cylinders, temp;
+
+	cylinders = 1024L;	/* Set number of cylinders to max */
+	sectors = 62L;		/* Maximize sectors per track */
+
+	temp = cylinders * sectors;	/* Compute divisor for heads */
+	heads = capacity / temp;	/* Compute value for number of heads */
+	if (capacity % temp) {	/* If no remainder, done! */
+		heads++;	/* Else, increment number of heads */
+		temp = cylinders * heads;	/* Compute divisor for sectors */
+		sectors = capacity / temp;	/* Compute value for sectors per
+						   track */
+		if (capacity % temp) {	/* If no remainder, done! */
+			sectors++;	/* Else, increment number of sectors */
+			temp = heads * sectors;		/* Compute divisor for cylinders */
+			cylinders = capacity / temp;	/* Compute number of cylinders */
+		}
+	}
+	if (cylinders == 0)
+		rv = (unsigned) -1;	/* Give error if 0 cylinders */
+
+	*cyls = (unsigned int) cylinders;	/* Stuff return values */
+	*secs = (unsigned int) sectors;
+	*hds = (unsigned int) heads;
+	return (rv);
+}
+
+/**
+ * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors.
+ * @disk: which device
+ * @capacity: size of the disk in sectors
+ * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders
+ *
+ * Description : determine the BIOS mapping/geometry used for a drive in a
+ *      SCSI-CAM system, storing the results in ip as required
+ *      by the HDIO_GETGEO ioctl().
+ *
+ * Returns : -1 on failure, 0 on success.
+ */
+int scsicam_bios_param(struct gendisk *disk, sector_t capacity, int *ip)
+{
+	u64 capacity64 = capacity;	/* Suppress gcc warning */
+	int ret = 0;
+
+	/* try to infer mapping from partition table */
+	if (scsi_partsize(disk, capacity, ip))
+		return 0;
+
+	if (capacity64 < (1ULL << 32)) {
+		/*
+		 * Pick some standard mapping with at most 1024 cylinders, and
+		 * at most 62 sectors per track - this works up to 7905 MB.
+		 */
+		ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,
+		       (unsigned int *)ip + 0, (unsigned int *)ip + 1);
+	}
+
+	/*
+	 * If something went wrong, then apparently we have to return a geometry
+	 * with more than 1024 cylinders.
+	 */
+	if (ret || ip[0] > 255 || ip[1] > 63) {
+		if ((capacity >> 11) > 65534) {
+			ip[0] = 255;
+			ip[1] = 63;
+		} else {
+			ip[0] = 64;
+			ip[1] = 32;
+		}
+
+		if (capacity > 65535*63*255)
+			ip[2] = 65535;
+		else
+			ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(scsicam_bios_param);