From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- net/ceph/striper.c | 278 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 278 insertions(+) create mode 100644 net/ceph/striper.c (limited to 'net/ceph/striper.c') diff --git a/net/ceph/striper.c b/net/ceph/striper.c new file mode 100644 index 000000000..2b8288858 --- /dev/null +++ b/net/ceph/striper.c @@ -0,0 +1,278 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include + +#include +#include + +#include +#include + +/* + * Map a file extent to a stripe unit within an object. + * Fill in objno, offset into object, and object extent length (i.e. the + * number of bytes mapped, less than or equal to @l->stripe_unit). + * + * Example for stripe_count = 3, stripes_per_object = 4: + * + * blockno | 0 3 6 9 | 1 4 7 10 | 2 5 8 11 | 12 15 18 21 | 13 16 19 + * stripeno | 0 1 2 3 | 0 1 2 3 | 0 1 2 3 | 4 5 6 7 | 4 5 6 + * stripepos | 0 | 1 | 2 | 0 | 1 + * objno | 0 | 1 | 2 | 3 | 4 + * objsetno | 0 | 1 + */ +void ceph_calc_file_object_mapping(struct ceph_file_layout *l, + u64 off, u64 len, + u64 *objno, u64 *objoff, u32 *xlen) +{ + u32 stripes_per_object = l->object_size / l->stripe_unit; + u64 blockno; /* which su in the file (i.e. globally) */ + u32 blockoff; /* offset into su */ + u64 stripeno; /* which stripe */ + u32 stripepos; /* which su in the stripe, + which object in the object set */ + u64 objsetno; /* which object set */ + u32 objsetpos; /* which stripe in the object set */ + + blockno = div_u64_rem(off, l->stripe_unit, &blockoff); + stripeno = div_u64_rem(blockno, l->stripe_count, &stripepos); + objsetno = div_u64_rem(stripeno, stripes_per_object, &objsetpos); + + *objno = objsetno * l->stripe_count + stripepos; + *objoff = objsetpos * l->stripe_unit + blockoff; + *xlen = min_t(u64, len, l->stripe_unit - blockoff); +} +EXPORT_SYMBOL(ceph_calc_file_object_mapping); + +/* + * Return the last extent with given objno (@object_extents is sorted + * by objno). If not found, return NULL and set @add_pos so that the + * new extent can be added with list_add(add_pos, new_ex). + */ +static struct ceph_object_extent * +lookup_last(struct list_head *object_extents, u64 objno, + struct list_head **add_pos) +{ + struct list_head *pos; + + list_for_each_prev(pos, object_extents) { + struct ceph_object_extent *ex = + list_entry(pos, typeof(*ex), oe_item); + + if (ex->oe_objno == objno) + return ex; + + if (ex->oe_objno < objno) + break; + } + + *add_pos = pos; + return NULL; +} + +static struct ceph_object_extent * +lookup_containing(struct list_head *object_extents, u64 objno, + u64 objoff, u32 xlen) +{ + struct ceph_object_extent *ex; + + list_for_each_entry(ex, object_extents, oe_item) { + if (ex->oe_objno == objno && + ex->oe_off <= objoff && + ex->oe_off + ex->oe_len >= objoff + xlen) /* paranoia */ + return ex; + + if (ex->oe_objno > objno) + break; + } + + return NULL; +} + +/* + * Map a file extent to a sorted list of object extents. + * + * We want only one (or as few as possible) object extents per object. + * Adjacent object extents will be merged together, each returned object + * extent may reverse map to multiple different file extents. + * + * Call @alloc_fn for each new object extent and @action_fn for each + * mapped stripe unit, whether it was merged into an already allocated + * object extent or started a new object extent. + * + * Newly allocated object extents are added to @object_extents. + * To keep @object_extents sorted, successive calls to this function + * must map successive file extents (i.e. the list of file extents that + * are mapped using the same @object_extents must be sorted). + * + * The caller is responsible for @object_extents. + */ +int ceph_file_to_extents(struct ceph_file_layout *l, u64 off, u64 len, + struct list_head *object_extents, + struct ceph_object_extent *alloc_fn(void *arg), + void *alloc_arg, + ceph_object_extent_fn_t action_fn, + void *action_arg) +{ + struct ceph_object_extent *last_ex, *ex; + + while (len) { + struct list_head *add_pos = NULL; + u64 objno, objoff; + u32 xlen; + + ceph_calc_file_object_mapping(l, off, len, &objno, &objoff, + &xlen); + + last_ex = lookup_last(object_extents, objno, &add_pos); + if (!last_ex || last_ex->oe_off + last_ex->oe_len != objoff) { + ex = alloc_fn(alloc_arg); + if (!ex) + return -ENOMEM; + + ex->oe_objno = objno; + ex->oe_off = objoff; + ex->oe_len = xlen; + if (action_fn) + action_fn(ex, xlen, action_arg); + + if (!last_ex) + list_add(&ex->oe_item, add_pos); + else + list_add(&ex->oe_item, &last_ex->oe_item); + } else { + last_ex->oe_len += xlen; + if (action_fn) + action_fn(last_ex, xlen, action_arg); + } + + off += xlen; + len -= xlen; + } + + for (last_ex = list_first_entry(object_extents, typeof(*ex), oe_item), + ex = list_next_entry(last_ex, oe_item); + &ex->oe_item != object_extents; + last_ex = ex, ex = list_next_entry(ex, oe_item)) { + if (last_ex->oe_objno > ex->oe_objno || + (last_ex->oe_objno == ex->oe_objno && + last_ex->oe_off + last_ex->oe_len >= ex->oe_off)) { + WARN(1, "%s: object_extents list not sorted!\n", + __func__); + return -EINVAL; + } + } + + return 0; +} +EXPORT_SYMBOL(ceph_file_to_extents); + +/* + * A stripped down, non-allocating version of ceph_file_to_extents(), + * for when @object_extents is already populated. + */ +int ceph_iterate_extents(struct ceph_file_layout *l, u64 off, u64 len, + struct list_head *object_extents, + ceph_object_extent_fn_t action_fn, + void *action_arg) +{ + while (len) { + struct ceph_object_extent *ex; + u64 objno, objoff; + u32 xlen; + + ceph_calc_file_object_mapping(l, off, len, &objno, &objoff, + &xlen); + + ex = lookup_containing(object_extents, objno, objoff, xlen); + if (!ex) { + WARN(1, "%s: objno %llu %llu~%u not found!\n", + __func__, objno, objoff, xlen); + return -EINVAL; + } + + action_fn(ex, xlen, action_arg); + + off += xlen; + len -= xlen; + } + + return 0; +} +EXPORT_SYMBOL(ceph_iterate_extents); + +/* + * Reverse map an object extent to a sorted list of file extents. + * + * On success, the caller is responsible for: + * + * kfree(file_extents) + */ +int ceph_extent_to_file(struct ceph_file_layout *l, + u64 objno, u64 objoff, u64 objlen, + struct ceph_file_extent **file_extents, + u32 *num_file_extents) +{ + u32 stripes_per_object = l->object_size / l->stripe_unit; + u64 blockno; /* which su */ + u32 blockoff; /* offset into su */ + u64 stripeno; /* which stripe */ + u32 stripepos; /* which su in the stripe, + which object in the object set */ + u64 objsetno; /* which object set */ + u32 i = 0; + + if (!objlen) { + *file_extents = NULL; + *num_file_extents = 0; + return 0; + } + + *num_file_extents = DIV_ROUND_UP_ULL(objoff + objlen, l->stripe_unit) - + DIV_ROUND_DOWN_ULL(objoff, l->stripe_unit); + *file_extents = kmalloc_objs(**file_extents, *num_file_extents, + GFP_NOIO); + if (!*file_extents) + return -ENOMEM; + + div_u64_rem(objoff, l->stripe_unit, &blockoff); + while (objlen) { + u64 off, len; + + objsetno = div_u64_rem(objno, l->stripe_count, &stripepos); + stripeno = div_u64(objoff, l->stripe_unit) + + objsetno * stripes_per_object; + blockno = stripeno * l->stripe_count + stripepos; + off = blockno * l->stripe_unit + blockoff; + len = min_t(u64, objlen, l->stripe_unit - blockoff); + + (*file_extents)[i].fe_off = off; + (*file_extents)[i].fe_len = len; + + blockoff = 0; + objoff += len; + objlen -= len; + i++; + } + + BUG_ON(i != *num_file_extents); + return 0; +} +EXPORT_SYMBOL(ceph_extent_to_file); + +u64 ceph_get_num_objects(struct ceph_file_layout *l, u64 size) +{ + u64 period = (u64)l->stripe_count * l->object_size; + u64 num_periods = DIV64_U64_ROUND_UP(size, period); + u64 remainder_bytes; + u64 remainder_objs = 0; + + div64_u64_rem(size, period, &remainder_bytes); + if (remainder_bytes > 0 && + remainder_bytes < (u64)l->stripe_count * l->stripe_unit) + remainder_objs = l->stripe_count - + DIV_ROUND_UP_ULL(remainder_bytes, l->stripe_unit); + + return num_periods * l->stripe_count - remainder_objs; +} +EXPORT_SYMBOL(ceph_get_num_objects); -- cgit v1.3.1