Commit 19138af1 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)

x86/unwind: Recover kretprobe trampoline entry

Since the kretprobe replaces the function return address with
the kretprobe_trampoline on the stack, x86 unwinders can not
continue the stack unwinding at that point, or record
kretprobe_trampoline instead of correct return address.

To fix this issue, find the correct return address from task's
kretprobe_instances as like as function-graph tracer does.

With this fix, the unwinder can correctly unwind the stack
from kretprobe event on x86, as below.

           <...>-135     [003] ...1     6.722338: r_full_proxy_read_0: (vfs_read+0xab/0x1a0 <- full_proxy_read)
           <...>-135     [003] ...1     6.722377: <stack trace>
 => kretprobe_trace_func+0x209/0x2f0
 => kretprobe_dispatcher+0x4a/0x70
 => __kretprobe_trampoline_handler+0xca/0x150
 => trampoline_handler+0x44/0x70
 => kretprobe_trampoline+0x2a/0x50
 => vfs_read+0xab/0x1a0
 => ksys_read+0x5f/0xe0
 => do_syscall_64+0x33/0x40
 => entry_SYSCALL_64_after_hwframe+0x44/0xae

Link: https://lkml.kernel.org/r/163163055130.489837.5161749078833497255.stgit@devnote2Reported-by: default avatarDaniel Xu <dxu@dxuuu.xyz>
Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Suggested-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Tested-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 1f368393
......@@ -4,6 +4,7 @@
#include <linux/sched.h>
#include <linux/ftrace.h>
#include <linux/kprobes.h>
#include <asm/ptrace.h>
#include <asm/stacktrace.h>
......@@ -15,6 +16,7 @@ struct unwind_state {
unsigned long stack_mask;
struct task_struct *task;
int graph_idx;
struct llist_node *kr_cur;
bool error;
#if defined(CONFIG_UNWINDER_ORC)
bool signal, full_regs;
......@@ -99,6 +101,27 @@ void unwind_module_init(struct module *mod, void *orc_ip, size_t orc_ip_size,
void *orc, size_t orc_size) {}
#endif
static inline
unsigned long unwind_recover_kretprobe(struct unwind_state *state,
unsigned long addr, unsigned long *addr_p)
{
return is_kretprobe_trampoline(addr) ?
kretprobe_find_ret_addr(state->task, addr_p, &state->kr_cur) :
addr;
}
/* Recover the return address modified by kretprobe and ftrace_graph. */
static inline
unsigned long unwind_recover_ret_addr(struct unwind_state *state,
unsigned long addr, unsigned long *addr_p)
{
unsigned long ret;
ret = ftrace_graph_ret_addr(state->task, &state->graph_idx,
addr, addr_p);
return unwind_recover_kretprobe(state, ret, addr_p);
}
/*
* This disables KASAN checking when reading a value from another task's stack,
* since the other task could be running on another CPU and could have poisoned
......
......@@ -240,8 +240,7 @@ static bool update_stack_state(struct unwind_state *state,
else {
addr_p = unwind_get_return_address_ptr(state);
addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
addr, addr_p);
state->ip = unwind_recover_ret_addr(state, addr, addr_p);
}
/* Save the original stack pointer for unwind_dump(): */
......
......@@ -15,8 +15,7 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
addr = READ_ONCE_NOCHECK(*state->sp);
return ftrace_graph_ret_addr(state->task, &state->graph_idx,
addr, state->sp);
return unwind_recover_ret_addr(state, addr, state->sp);
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);
......
......@@ -534,9 +534,8 @@ bool unwind_next_frame(struct unwind_state *state)
if (!deref_stack_reg(state, ip_p, &state->ip))
goto err;
state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
state->ip, (void *)ip_p);
state->ip = unwind_recover_ret_addr(state, state->ip,
(unsigned long *)ip_p);
state->sp = sp;
state->regs = NULL;
state->prev_regs = NULL;
......@@ -549,7 +548,18 @@ bool unwind_next_frame(struct unwind_state *state)
(void *)orig_ip);
goto err;
}
/*
* There is a small chance to interrupt at the entry of
* __kretprobe_trampoline() where the ORC info doesn't exist.
* That point is right after the RET to __kretprobe_trampoline()
* which was modified return address.
* At that point, the @addr_p of the unwind_recover_kretprobe()
* (this has to point the address of the stack entry storing
* the modified return address) must be "SP - (a stack entry)"
* because SP is incremented by the RET.
*/
state->ip = unwind_recover_kretprobe(state, state->ip,
(unsigned long *)(state->sp - sizeof(long)));
state->regs = (struct pt_regs *)sp;
state->prev_regs = NULL;
state->full_regs = true;
......@@ -562,6 +572,9 @@ bool unwind_next_frame(struct unwind_state *state)
(void *)orig_ip);
goto err;
}
/* See UNWIND_HINT_TYPE_REGS case comment. */
state->ip = unwind_recover_kretprobe(state, state->ip,
(unsigned long *)(state->sp - sizeof(long)));
if (state->full_regs)
state->prev_regs = state->regs;
......
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