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Subject[PATCH 1/5] uprobes: kill pre_ssout(), introduce set_xol_ip()
No functional changes, preparation.

- Do not change regs->ip in pre_xol().

- Kill pre_ssout(), move its code into the single caller.

- Add the new __weak helper, set_xol_ip(). Currently it simply does
regs->ip = utask->xol_vaddr.

- Change uprobe_notify_resume() to do set_xol_ip() after pre_xol().

IOW, before this patch uprobe_notify_resume() does:

utask->state = UTASK_SSTEP;
pre_ssout:
xol_get_insn_slot();
pre_xol(); // <----- sets regs->ip
user_enable_single_step(current);

after:

xol_get_insn_slot();
pre_xol(); // <------ doesn't change regs->ip
user_enable_single_step(current);
utask->state = UTASK_SSTEP;
set_xol_ip(); // <----- sets regs->ip

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
arch/x86/kernel/uprobes.c | 2 --
include/linux/uprobes.h | 1 +
kernel/uprobes.c | 27 +++++++++++++--------------
3 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 40f9f75..cd086be 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -429,7 +429,6 @@ int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
tskinfo->saved_trap_no = current->thread.trap_no;
current->thread.trap_no = UPROBE_TRAP_NO;

- regs->ip = current->utask->xol_vaddr;
if (uprobe->fixups & UPROBES_FIX_RIP_AX) {
tskinfo->saved_scratch_register = regs->ax;
regs->ax = current->utask->vaddr;
@@ -449,7 +448,6 @@ int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
tskinfo->saved_trap_no = current->thread.trap_no;
current->thread.trap_no = UPROBE_TRAP_NO;

- regs->ip = current->utask->xol_vaddr;
return 0;
}
#endif
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 20bdd0a..c9ff67a 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -140,6 +140,7 @@ extern int uprobe_bkpt_notifier(struct pt_regs *regs);
extern void uprobe_notify_resume(struct pt_regs *regs);
extern bool uprobe_deny_signal(void);
extern bool __weak can_skip_xol(struct pt_regs *regs, struct uprobe *u);
+extern void __weak set_xol_ip(struct pt_regs *regs);
#else /* CONFIG_UPROBES is not defined */
static inline int register_uprobe(struct inode *inode, loff_t offset,
struct uprobe_consumer *consumer)
diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index 2493191..b596432 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -1311,15 +1311,6 @@ static struct uprobe_task *add_utask(void)
return utask;
}

-/* Prepare to single-step probed instruction out of line. */
-static int pre_ssout(struct uprobe *uprobe, struct pt_regs *regs,
- unsigned long vaddr)
-{
- if (xol_get_insn_slot(uprobe, vaddr) && !pre_xol(uprobe, regs))
- return 0;
- return -EFAULT;
-}
-
bool uprobe_deny_signal(void)
{
struct task_struct *tsk = current;
@@ -1351,6 +1342,11 @@ bool __weak can_skip_xol(struct pt_regs *regs, struct uprobe *u)
return false;
}

+void __weak set_xol_ip(struct pt_regs *regs)
+{
+ set_instruction_pointer(regs, current->utask->xol_vaddr);
+}
+
/*
* uprobe_notify_resume gets called in task context just before returning
* to userspace.
@@ -1396,12 +1392,15 @@ void uprobe_notify_resume(struct pt_regs *regs)
if (u->flags & UPROBES_SKIP_SSTEP && can_skip_xol(regs, u))
goto cleanup_ret;

- utask->state = UTASK_SSTEP;
- if (!pre_ssout(u, regs, probept))
- user_enable_single_step(current);
- else
- /* Cannot Singlestep; re-execute the instruction. */
+ if (!xol_get_insn_slot(u, probept))
+ goto cleanup_ret;
+
+ if (pre_xol(u, regs))
goto cleanup_ret;
+
+ user_enable_single_step(current);
+ utask->state = UTASK_SSTEP;
+ set_xol_ip(regs);
} else {
u = utask->active_uprobe;
if (utask->state == UTASK_SSTEP_ACK)
--
1.5.5.1



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