Quelle rseq.c Sprache: C

// SPDX-License-Identifier: GPL-2.0+
/*
* Restartable sequences system call
*
* Copyright (C) 2015, Google, Inc.,
* Paul Turner <pjt@google.com> and Andrew Hunter <ahh@google.com>
* Copyright (C) 2015-2018, EfficiOS Inc.,
* Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
*/

#include <linux/sched.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/rseq.h>
#include <linux/types.h>
#include <linux/ratelimit.h>
#include <asm/ptrace.h>

#define CREATE_TRACE_POINTS
#include <trace/events/rseq.h>

/* The original rseq structure size (including padding) is 32 bytes. */
#define ORIG_RSEQ_SIZE  32

#define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \
      RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \
      RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE)

#ifdef CONFIG_DEBUG_RSEQ
static struct rseq *rseq_kernel_fields(struct task_struct *t)
{
return (struct rseq *) t->rseq_fields;
}

static int rseq_validate_ro_fields(struct task_struct *t)
{
static DEFINE_RATELIMIT_STATE(_rs,
          DEFAULT_RATELIMIT_INTERVAL,
          DEFAULT_RATELIMIT_BURST);
u32 cpu_id_start, cpu_id, node_id, mm_cid;
struct rseq __user *rseq = t->rseq;

/*
* Validate fields which are required to be read-only by
* user-space.
*/
if (!user_read_access_begin(rseq, t->rseq_len))
  goto efault;
unsafe_get_user(cpu_id_start, &rseq->cpu_id_start, efault_end);
unsafe_get_user(cpu_id, &rseq->cpu_id, efault_end);
unsafe_get_user(node_id, &rseq->node_id, efault_end);
unsafe_get_user(mm_cid, &rseq->mm_cid, efault_end);
user_read_access_end();

if ((cpu_id_start != rseq_kernel_fields(t)->cpu_id_start ||
     cpu_id != rseq_kernel_fields(t)->cpu_id ||
     node_id != rseq_kernel_fields(t)->node_id ||
     mm_cid != rseq_kernel_fields(t)->mm_cid) && __ratelimit(&_rs)) {

  pr_warn("Detected rseq corruption for pid: %d, name: %s\n"
   "\tcpu_id_start: %u ?= %u\n"
   "\tcpu_id: %u ?= %u\n"
   "\tnode_id: %u ?= %u\n"
   "\tmm_cid: %u ?= %u\n",
   t->pid, t->comm,
   cpu_id_start, rseq_kernel_fields(t)->cpu_id_start,
   cpu_id, rseq_kernel_fields(t)->cpu_id,
   node_id, rseq_kernel_fields(t)->node_id,
   mm_cid, rseq_kernel_fields(t)->mm_cid);
}

/* For now, only print a console warning on mismatch. */
return 0;

efault_end:
user_read_access_end();
efault:
return -EFAULT;
}

/*
* Update an rseq field and its in-kernel copy in lock-step to keep a coherent
* state.
*/
#define rseq_unsafe_put_user(t, value, field, error_label)  \
do {        \
  unsafe_put_user(value, &t->rseq->field, error_label); \
  rseq_kernel_fields(t)->field = value;   \
} while (0)

#else
static int rseq_validate_ro_fields(struct task_struct *t)
{
return 0;
}

#define rseq_unsafe_put_user(t, value, field, error_label)  \
unsafe_put_user(value, &t->rseq->field, error_label)
#endif

/*
*
* Restartable sequences are a lightweight interface that allows
* user-level code to be executed atomically relative to scheduler
* preemption and signal delivery. Typically used for implementing
* per-cpu operations.
*
* It allows user-space to perform update operations on per-cpu data
* without requiring heavy-weight atomic operations.
*
* Detailed algorithm of rseq user-space assembly sequences:
*
*                     init(rseq_cs)
*                     cpu = TLS->rseq::cpu_id_start
*   [1]               TLS->rseq::rseq_cs = rseq_cs
*   [start_ip]        ----------------------------
*   [2]               if (cpu != TLS->rseq::cpu_id)
*                             goto abort_ip;
*   [3]               <last_instruction_in_cs>
*   [post_commit_ip]  ----------------------------
*
*   The address of jump target abort_ip must be outside the critical
*   region, i.e.:
*
*     [abort_ip] < [start_ip]  || [abort_ip] >= [post_commit_ip]
*
*   Steps [2]-[3] (inclusive) need to be a sequence of instructions in
*   userspace that can handle being interrupted between any of those
*   instructions, and then resumed to the abort_ip.
*
*   1.  Userspace stores the address of the struct rseq_cs assembly
*       block descriptor into the rseq_cs field of the registered
*       struct rseq TLS area. This update is performed through a single
*       store within the inline assembly instruction sequence.
*       [start_ip]
*
*   2.  Userspace tests to check whether the current cpu_id field match
*       the cpu number loaded before start_ip, branching to abort_ip
*       in case of a mismatch.
*
*       If the sequence is preempted or interrupted by a signal
*       at or after start_ip and before post_commit_ip, then the kernel
*       clears TLS->__rseq_abi::rseq_cs, and sets the user-space return
*       ip to abort_ip before returning to user-space, so the preempted
*       execution resumes at abort_ip.
*
*   3.  Userspace critical section final instruction before
*       post_commit_ip is the commit. The critical section is
*       self-terminating.
*       [post_commit_ip]
*
*   4.  <success>
*
*   On failure at [2], or if interrupted by preempt or signal delivery
*   between [1] and [3]:
*
*       [abort_ip]
*   F1. <failure>
*/

static int rseq_update_cpu_node_id(struct task_struct *t)
{
struct rseq __user *rseq = t->rseq;
u32 cpu_id = raw_smp_processor_id();
u32 node_id = cpu_to_node(cpu_id);
u32 mm_cid = task_mm_cid(t);

/*
* Validate read-only rseq fields.
*/
if (rseq_validate_ro_fields(t))
  goto efault;
WARN_ON_ONCE((int) mm_cid < 0);
if (!user_write_access_begin(rseq, t->rseq_len))
  goto efault;

rseq_unsafe_put_user(t, cpu_id, cpu_id_start, efault_end);
rseq_unsafe_put_user(t, cpu_id, cpu_id, efault_end);
rseq_unsafe_put_user(t, node_id, node_id, efault_end);
rseq_unsafe_put_user(t, mm_cid, mm_cid, efault_end);

/*
* Additional feature fields added after ORIG_RSEQ_SIZE
* need to be conditionally updated only if
* t->rseq_len != ORIG_RSEQ_SIZE.
*/
user_write_access_end();
trace_rseq_update(t);
return 0;

efault_end:
user_write_access_end();
efault:
return -EFAULT;
}

static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
{
struct rseq __user *rseq = t->rseq;
u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED, node_id = 0,
     mm_cid = 0;

/*
* Validate read-only rseq fields.
*/
if (rseq_validate_ro_fields(t))
  goto efault;

if (!user_write_access_begin(rseq, t->rseq_len))
  goto efault;

/*
* Reset all fields to their initial state.
*
* All fields have an initial state of 0 except cpu_id which is set to
* RSEQ_CPU_ID_UNINITIALIZED, so that any user coming in after
* unregistration can figure out that rseq needs to be registered
* again.
*/
rseq_unsafe_put_user(t, cpu_id_start, cpu_id_start, efault_end);
rseq_unsafe_put_user(t, cpu_id, cpu_id, efault_end);
rseq_unsafe_put_user(t, node_id, node_id, efault_end);
rseq_unsafe_put_user(t, mm_cid, mm_cid, efault_end);

/*
* Additional feature fields added after ORIG_RSEQ_SIZE
* need to be conditionally reset only if
* t->rseq_len != ORIG_RSEQ_SIZE.
*/
user_write_access_end();
return 0;

efault_end:
user_write_access_end();
efault:
return -EFAULT;
}

/*
* Get the user-space pointer value stored in the 'rseq_cs' field.
*/
static int rseq_get_rseq_cs_ptr_val(struct rseq __user *rseq, u64 *rseq_cs)
{
if (!rseq_cs)
  return -EFAULT;

#ifdef CONFIG_64BIT
if (get_user(*rseq_cs, &rseq->rseq_cs))
  return -EFAULT;
#else
if (copy_from_user(rseq_cs, &rseq->rseq_cs, sizeof(*rseq_cs)))
  return -EFAULT;
#endif

return 0;
}

/*
* If the rseq_cs field of 'struct rseq' contains a valid pointer to
* user-space, copy 'struct rseq_cs' from user-space and validate its fields.
*/
static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
{
struct rseq_cs __user *urseq_cs;
u64 ptr;
u32 __user *usig;
u32 sig;
int ret;

ret = rseq_get_rseq_cs_ptr_val(t->rseq, &ptr);
if (ret)
  return ret;

/* If the rseq_cs pointer is NULL, return a cleared struct rseq_cs. */
if (!ptr) {
  memset(rseq_cs, 0, sizeof(*rseq_cs));
  return 0;
}
/* Check that the pointer value fits in the user-space process space. */
if (ptr >= TASK_SIZE)
  return -EINVAL;
urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr;
if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
  return -EFAULT;

if (rseq_cs->start_ip >= TASK_SIZE ||
     rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE ||
     rseq_cs->abort_ip >= TASK_SIZE ||
     rseq_cs->version > 0)
  return -EINVAL;
/* Check for overflow. */
if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip)
  return -EINVAL;
/* Ensure that abort_ip is not in the critical section. */
if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset)
  return -EINVAL;

usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
ret = get_user(sig, usig);
if (ret)
  return ret;

if (current->rseq_sig != sig) {
  printk_ratelimited(KERN_WARNING
   "Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n",
   sig, current->rseq_sig, current->pid, usig);
  return -EINVAL;
}
return 0;
}

static bool rseq_warn_flags(const char *str, u32 flags)
{
u32 test_flags;

if (!flags)
  return false;
test_flags = flags & RSEQ_CS_NO_RESTART_FLAGS;
if (test_flags)
  pr_warn_once("Deprecated flags (%u) in %s ABI structure", test_flags, str);
test_flags = flags & ~RSEQ_CS_NO_RESTART_FLAGS;
if (test_flags)
  pr_warn_once("Unknown flags (%u) in %s ABI structure", test_flags, str);
return true;
}

static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
{
u32 flags, event_mask;
int ret;

if (rseq_warn_flags("rseq_cs", cs_flags))
  return -EINVAL;

/* Get thread flags. */
ret = get_user(flags, &t->rseq->flags);
if (ret)
  return ret;

if (rseq_warn_flags("rseq", flags))
  return -EINVAL;

/*
* Load and clear event mask atomically with respect to
* scheduler preemption and membarrier IPIs.
*/
scoped_guard(RSEQ_EVENT_GUARD) {
  event_mask = t->rseq_event_mask;
  t->rseq_event_mask = 0;
}

return !!event_mask;
}

static int clear_rseq_cs(struct rseq __user *rseq)
{
/*
* The rseq_cs field is set to NULL on preemption or signal
* delivery on top of rseq assembly block, as well as on top
* of code outside of the rseq assembly block. This performs
* a lazy clear of the rseq_cs field.
*
* Set rseq_cs to NULL.
*/
#ifdef CONFIG_64BIT
return put_user(0UL, &rseq->rseq_cs);
#else
if (clear_user(&rseq->rseq_cs, sizeof(rseq->rseq_cs)))
  return -EFAULT;
return 0;
#endif
}

/*
* Unsigned comparison will be true when ip >= start_ip, and when
* ip < start_ip + post_commit_offset.
*/
static bool in_rseq_cs(unsigned long ip, struct rseq_cs *rseq_cs)
{
return ip - rseq_cs->start_ip < rseq_cs->post_commit_offset;
}

static int rseq_ip_fixup(struct pt_regs *regs)
{
unsigned long ip = instruction_pointer(regs);
struct task_struct *t = current;
struct rseq_cs rseq_cs;
int ret;

ret = rseq_get_rseq_cs(t, &rseq_cs);
if (ret)
  return ret;

/*
* Handle potentially not being within a critical section.
* If not nested over a rseq critical section, restart is useless.
* Clear the rseq_cs pointer and return.
*/
if (!in_rseq_cs(ip, &rseq_cs))
  return clear_rseq_cs(t->rseq);
ret = rseq_need_restart(t, rseq_cs.flags);
if (ret <= 0)
  return ret;
ret = clear_rseq_cs(t->rseq);
if (ret)
  return ret;
trace_rseq_ip_fixup(ip, rseq_cs.start_ip, rseq_cs.post_commit_offset,
       rseq_cs.abort_ip);
instruction_pointer_set(regs, (unsigned long)rseq_cs.abort_ip);
return 0;
}

/*
* This resume handler must always be executed between any of:
* - preemption,
* - signal delivery,
* and return to user-space.
*
* This is how we can ensure that the entire rseq critical section
* will issue the commit instruction only if executed atomically with
* respect to other threads scheduled on the same CPU, and with respect
* to signal handlers.
*/
void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
{
struct task_struct *t = current;
int ret, sig;

if (unlikely(t->flags & PF_EXITING))
  return;

/*
* regs is NULL if and only if the caller is in a syscall path.  Skip
* fixup and leave rseq_cs as is so that rseq_sycall() will detect and
* kill a misbehaving userspace on debug kernels.
*/
if (regs) {
  ret = rseq_ip_fixup(regs);
  if (unlikely(ret < 0))
   goto error;
}
if (unlikely(rseq_update_cpu_node_id(t)))
  goto error;
return;

error:
sig = ksig ? ksig->sig : 0;
force_sigsegv(sig);
}

#ifdef CONFIG_DEBUG_RSEQ

/*
* Terminate the process if a syscall is issued within a restartable
* sequence.
*/
void rseq_syscall(struct pt_regs *regs)
{
unsigned long ip = instruction_pointer(regs);
struct task_struct *t = current;
struct rseq_cs rseq_cs;

if (!t->rseq)
  return;
if (rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
  force_sig(SIGSEGV);
}

#endif

/*
* sys_rseq - setup restartable sequences for caller thread.
*/
SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
  int, flags, u32, sig)
{
int ret;
u64 rseq_cs;

if (flags & RSEQ_FLAG_UNREGISTER) {
  if (flags & ~RSEQ_FLAG_UNREGISTER)
   return -EINVAL;
  /* Unregister rseq for current thread. */
  if (current->rseq != rseq || !current->rseq)
   return -EINVAL;
  if (rseq_len != current->rseq_len)
   return -EINVAL;
  if (current->rseq_sig != sig)
   return -EPERM;
  ret = rseq_reset_rseq_cpu_node_id(current);
  if (ret)
   return ret;
  current->rseq = NULL;
  current->rseq_sig = 0;
  current->rseq_len = 0;
  return 0;
}

if (unlikely(flags))
  return -EINVAL;

if (current->rseq) {
  /*
* If rseq is already registered, check whether
* the provided address differs from the prior
* one.
*/
  if (current->rseq != rseq || rseq_len != current->rseq_len)
   return -EINVAL;
  if (current->rseq_sig != sig)
   return -EPERM;
  /* Already registered. */
  return -EBUSY;
}

/*
* If there was no rseq previously registered, ensure the provided rseq
* is properly aligned, as communcated to user-space through the ELF
* auxiliary vector AT_RSEQ_ALIGN. If rseq_len is the original rseq
* size, the required alignment is the original struct rseq alignment.
*
* In order to be valid, rseq_len is either the original rseq size, or
* large enough to contain all supported fields, as communicated to
* user-space through the ELF auxiliary vector AT_RSEQ_FEATURE_SIZE.
*/
if (rseq_len < ORIG_RSEQ_SIZE ||
     (rseq_len == ORIG_RSEQ_SIZE && !IS_ALIGNED((unsigned long)rseq, ORIG_RSEQ_SIZE)) ||
     (rseq_len != ORIG_RSEQ_SIZE && (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) ||
         rseq_len < offsetof(struct rseq, end))))
  return -EINVAL;
if (!access_ok(rseq, rseq_len))
  return -EFAULT;

/*
* If the rseq_cs pointer is non-NULL on registration, clear it to
* avoid a potential segfault on return to user-space. The proper thing
* to do would have been to fail the registration but this would break
* older libcs that reuse the rseq area for new threads without
* clearing the fields.
*/
if (rseq_get_rseq_cs_ptr_val(rseq, &rseq_cs))
         return -EFAULT;
if (rseq_cs && clear_rseq_cs(rseq))
  return -EFAULT;

#ifdef CONFIG_DEBUG_RSEQ
/*
* Initialize the in-kernel rseq fields copy for validation of
* read-only fields.
*/
if (get_user(rseq_kernel_fields(current)->cpu_id_start, &rseq->cpu_id_start) ||
     get_user(rseq_kernel_fields(current)->cpu_id, &rseq->cpu_id) ||
     get_user(rseq_kernel_fields(current)->node_id, &rseq->node_id) ||
     get_user(rseq_kernel_fields(current)->mm_cid, &rseq->mm_cid))
  return -EFAULT;
#endif
/*
* Activate the registration by setting the rseq area address, length
* and signature in the task struct.
*/
current->rseq = rseq;
current->rseq_len = rseq_len;
current->rseq_sig = sig;

/*
* If rseq was previously inactive, and has just been
* registered, ensure the cpu_id_start and cpu_id fields
* are updated before returning to user-space.
*/
rseq_set_notify_resume(current);

return 0;
}

quality92%

¤ Dauer der Verarbeitung: 0.27 Sekunden (vorverarbeitet) ¤

Wurzel

Suchen

Beweissystem der NASA

Beweissystem Isabelle

NIST Cobol Testsuite

Cephes Mathematical Library

Wiener Entwicklungsmethode

Haftungshinweis

Die Informationen auf dieser Webseite wurden nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit, noch Qualität der bereit gestellten Informationen zugesichert.

Bemerkung:

Die farbliche Syntaxdarstellung ist noch experimentell.