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7eaf51a2e0
linux/kernel/stacktrace.c
Joe Lawrence 7eaf51a2e0 stacktrace: Unbreak stack_trace_save_tsk_reliable() 
Miroslav reported that the livepatch self-tests were failing, specifically
a case in which the consistency model ensures that a current executing
function is not allowed to be patched, "TEST: busy target module".

Recent renovations of stack_trace_save_tsk_reliable() left it returning
only an -ERRNO success indication in some configuration combinations:

  klp_check_stack()
    ret = stack_trace_save_tsk_reliable()
      #ifdef CONFIG_ARCH_STACKWALK && CONFIG_HAVE_RELIABLE_STACKTRACE
        stack_trace_save_tsk_reliable()
          ret = arch_stack_walk_reliable()
            return 0
            return -EINVAL
          ...
          return ret;
    ...
    if (ret < 0)
      /* stack_trace_save_tsk_reliable error */
    nr_entries = ret;                               << 0

Previously (and currently for !CONFIG_ARCH_STACKWALK &&
CONFIG_HAVE_RELIABLE_STACKTRACE) stack_trace_save_tsk_reliable() returned
the number of entries that it consumed in the passed storage array.

In the case of the above config and trace, be sure to return the
stacktrace_cookie.len on stack_trace_save_tsk_reliable() success.

Fixes: 25e39e32b0 ("livepatch: Simplify stack trace retrieval")
Reported-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: live-patching@vger.kernel.org
Cc: jikos@kernel.org
Cc: pmladek@suse.com
Link: https://lkml.kernel.org/r/20190517185117.24642-1-joe.lawrence@redhat.com
2019-05-19 11:43:22 +02:00

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/*
* kernel/stacktrace.c
*
* Stack trace management functions
*
* Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
*/
#include <linux/sched/task_stack.h>
#include <linux/sched/debug.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/kallsyms.h>
#include <linux/stacktrace.h>
/**
* stack_trace_print - Print the entries in the stack trace
* @entries: Pointer to storage array
* @nr_entries: Number of entries in the storage array
* @spaces: Number of leading spaces to print
*/
void stack_trace_print(unsigned long *entries, unsigned int nr_entries,
int spaces)
{
unsigned int i;
if (WARN_ON(!entries))
return;
for (i = 0; i < nr_entries; i++)
printk("%*c%pS\n", 1 + spaces, ' ', (void *)entries[i]);
}
EXPORT_SYMBOL_GPL(stack_trace_print);
/**
* stack_trace_snprint - Print the entries in the stack trace into a buffer
* @buf: Pointer to the print buffer
* @size: Size of the print buffer
* @entries: Pointer to storage array
* @nr_entries: Number of entries in the storage array
* @spaces: Number of leading spaces to print
*
* Return: Number of bytes printed.
*/
int stack_trace_snprint(char *buf, size_t size, unsigned long *entries,
unsigned int nr_entries, int spaces)
{
unsigned int generated, i, total = 0;
if (WARN_ON(!entries))
return 0;
for (i = 0; i < nr_entries && size; i++) {
generated = snprintf(buf, size, "%*c%pS\n", 1 + spaces, ' ',
(void *)entries[i]);
total += generated;
if (generated >= size) {
buf += size;
size = 0;
} else {
buf += generated;
size -= generated;
}
}
return total;
}
EXPORT_SYMBOL_GPL(stack_trace_snprint);
#ifdef CONFIG_ARCH_STACKWALK
struct stacktrace_cookie {
unsigned long *store;
unsigned int size;
unsigned int skip;
unsigned int len;
};
static bool stack_trace_consume_entry(void *cookie, unsigned long addr,
bool reliable)
{
struct stacktrace_cookie *c = cookie;
if (c->len >= c->size)
return false;
if (c->skip > 0) {
c->skip--;
return true;
}
c->store[c->len++] = addr;
return c->len < c->size;
}
static bool stack_trace_consume_entry_nosched(void *cookie, unsigned long addr,
bool reliable)
{
if (in_sched_functions(addr))
return true;
return stack_trace_consume_entry(cookie, addr, reliable);
}
/**
* stack_trace_save - Save a stack trace into a storage array
* @store: Pointer to storage array
* @size: Size of the storage array
* @skipnr: Number of entries to skip at the start of the stack trace
*
* Return: Number of trace entries stored.
*/
unsigned int stack_trace_save(unsigned long *store, unsigned int size,
unsigned int skipnr)
{
stack_trace_consume_fn consume_entry = stack_trace_consume_entry;
struct stacktrace_cookie c = {
.store = store,
.size = size,
.skip = skipnr + 1,
};
arch_stack_walk(consume_entry, &c, current, NULL);
return c.len;
}
EXPORT_SYMBOL_GPL(stack_trace_save);
/**
* stack_trace_save_tsk - Save a task stack trace into a storage array
* @task: The task to examine
* @store: Pointer to storage array
* @size: Size of the storage array
* @skipnr: Number of entries to skip at the start of the stack trace
*
* Return: Number of trace entries stored.
*/
unsigned int stack_trace_save_tsk(struct task_struct *tsk, unsigned long *store,
unsigned int size, unsigned int skipnr)
{
stack_trace_consume_fn consume_entry = stack_trace_consume_entry_nosched;
struct stacktrace_cookie c = {
.store = store,
.size = size,
.skip = skipnr + 1,
};
if (!try_get_task_stack(tsk))
return 0;
arch_stack_walk(consume_entry, &c, tsk, NULL);
put_task_stack(tsk);
return c.len;
}
/**
* stack_trace_save_regs - Save a stack trace based on pt_regs into a storage array
* @regs: Pointer to pt_regs to examine
* @store: Pointer to storage array
* @size: Size of the storage array
* @skipnr: Number of entries to skip at the start of the stack trace
*
* Return: Number of trace entries stored.
*/
unsigned int stack_trace_save_regs(struct pt_regs *regs, unsigned long *store,
unsigned int size, unsigned int skipnr)
{
stack_trace_consume_fn consume_entry = stack_trace_consume_entry;
struct stacktrace_cookie c = {
.store = store,
.size = size,
.skip = skipnr,
};
arch_stack_walk(consume_entry, &c, current, regs);
return c.len;
}
#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
/**
* stack_trace_save_tsk_reliable - Save task stack with verification
* @tsk: Pointer to the task to examine
* @store: Pointer to storage array
* @size: Size of the storage array
*
* Return: An error if it detects any unreliable features of the
* stack. Otherwise it guarantees that the stack trace is
* reliable and returns the number of entries stored.
*
* If the task is not 'current', the caller *must* ensure the task is inactive.
*/
int stack_trace_save_tsk_reliable(struct task_struct *tsk, unsigned long *store,
unsigned int size)
{
stack_trace_consume_fn consume_entry = stack_trace_consume_entry;
struct stacktrace_cookie c = {
.store = store,
.size = size,
};
int ret;
/*
* If the task doesn't have a stack (e.g., a zombie), the stack is
* "reliably" empty.
*/
if (!try_get_task_stack(tsk))
return 0;
ret = arch_stack_walk_reliable(consume_entry, &c, tsk);
put_task_stack(tsk);
return ret ? ret : c.len;
}
#endif
#ifdef CONFIG_USER_STACKTRACE_SUPPORT
/**
* stack_trace_save_user - Save a user space stack trace into a storage array
* @store: Pointer to storage array
* @size: Size of the storage array
*
* Return: Number of trace entries stored.
*/
unsigned int stack_trace_save_user(unsigned long *store, unsigned int size)
{
stack_trace_consume_fn consume_entry = stack_trace_consume_entry;
struct stacktrace_cookie c = {
.store = store,
.size = size,
};
/* Trace user stack if not a kernel thread */
if (!current->mm)
return 0;
arch_stack_walk_user(consume_entry, &c, task_pt_regs(current));
return c.len;
}
#endif
#else /* CONFIG_ARCH_STACKWALK */
/*
* Architectures that do not implement save_stack_trace_*()
* get these weak aliases and once-per-bootup warnings
* (whenever this facility is utilized - for example by procfs):
*/
__weak void
save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
{
WARN_ONCE(1, KERN_INFO "save_stack_trace_tsk() not implemented yet.\n");
}
__weak void
save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
{
WARN_ONCE(1, KERN_INFO "save_stack_trace_regs() not implemented yet.\n");
}
__weak int
save_stack_trace_tsk_reliable(struct task_struct *tsk,
struct stack_trace *trace)
{
WARN_ONCE(1, KERN_INFO "save_stack_tsk_reliable() not implemented yet.\n");
return -ENOSYS;
}
/**
* stack_trace_save - Save a stack trace into a storage array
* @store: Pointer to storage array
* @size: Size of the storage array
* @skipnr: Number of entries to skip at the start of the stack trace
*
* Return: Number of trace entries stored
*/
unsigned int stack_trace_save(unsigned long *store, unsigned int size,
unsigned int skipnr)
{
struct stack_trace trace = {
.entries = store,
.max_entries = size,
.skip = skipnr + 1,
};
save_stack_trace(&trace);
return trace.nr_entries;
}
EXPORT_SYMBOL_GPL(stack_trace_save);
/**
* stack_trace_save_tsk - Save a task stack trace into a storage array
* @task: The task to examine
* @store: Pointer to storage array
* @size: Size of the storage array
* @skipnr: Number of entries to skip at the start of the stack trace
*
* Return: Number of trace entries stored
*/
unsigned int stack_trace_save_tsk(struct task_struct *task,
unsigned long *store, unsigned int size,
unsigned int skipnr)
{
struct stack_trace trace = {
.entries = store,
.max_entries = size,
.skip = skipnr + 1,
};
save_stack_trace_tsk(task, &trace);
return trace.nr_entries;
}
/**
* stack_trace_save_regs - Save a stack trace based on pt_regs into a storage array
* @regs: Pointer to pt_regs to examine
* @store: Pointer to storage array
* @size: Size of the storage array
* @skipnr: Number of entries to skip at the start of the stack trace
*
* Return: Number of trace entries stored
*/
unsigned int stack_trace_save_regs(struct pt_regs *regs, unsigned long *store,
unsigned int size, unsigned int skipnr)
{
struct stack_trace trace = {
.entries = store,
.max_entries = size,
.skip = skipnr,
};
save_stack_trace_regs(regs, &trace);
return trace.nr_entries;
}
#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
/**
* stack_trace_save_tsk_reliable - Save task stack with verification
* @tsk: Pointer to the task to examine
* @store: Pointer to storage array
* @size: Size of the storage array
*
* Return: An error if it detects any unreliable features of the
* stack. Otherwise it guarantees that the stack trace is
* reliable and returns the number of entries stored.
*
* If the task is not 'current', the caller *must* ensure the task is inactive.
*/
int stack_trace_save_tsk_reliable(struct task_struct *tsk, unsigned long *store,
unsigned int size)
{
struct stack_trace trace = {
.entries = store,
.max_entries = size,
};
int ret = save_stack_trace_tsk_reliable(tsk, &trace);
return ret ? ret : trace.nr_entries;
}
#endif
#ifdef CONFIG_USER_STACKTRACE_SUPPORT
/**
* stack_trace_save_user - Save a user space stack trace into a storage array
* @store: Pointer to storage array
* @size: Size of the storage array
*
* Return: Number of trace entries stored
*/
unsigned int stack_trace_save_user(unsigned long *store, unsigned int size)
{
struct stack_trace trace = {
.entries = store,
.max_entries = size,
};
save_stack_trace_user(&trace);
return trace.nr_entries;
}
#endif /* CONFIG_USER_STACKTRACE_SUPPORT */
#endif /* !CONFIG_ARCH_STACKWALK */
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