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Subject[PATCH 4/7] uprobes: Do not play with utask in xol_get_insn_slot()
pre_ssout()->xol_get_insn_slot() path is confusing and buggy. This patch
cleanups the code, the next one fixes the bug.

Change xol_get_insn_slot() to only allocate the slot and do nothing more,
move the initialization of utask->xol_vaddr/vaddr into pre_ssout().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/events/uprobes.c | 37 +++++++++++++++++++++----------------
1 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index b09b3ba..2ed6239 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1176,30 +1176,26 @@ static unsigned long xol_take_insn_slot(struct xol_area *area)
}

/*
- * xol_get_insn_slot - If was not allocated a slot, then
- * allocate a slot.
+ * xol_get_insn_slot - allocate a slot for xol.
* Returns the allocated slot address or 0.
*/
-static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot_addr)
+static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
{
struct xol_area *area;
unsigned long offset;
+ unsigned long xol_vaddr;
void *vaddr;

area = get_xol_area();
if (!area)
return 0;

- current->utask->xol_vaddr = xol_take_insn_slot(area);
- /*
- * Initialize the slot if xol_vaddr points to valid
- * instruction slot.
- */
- if (unlikely(!current->utask->xol_vaddr))
+ xol_vaddr = xol_take_insn_slot(area);
+ if (unlikely(!xol_vaddr))
return 0;

- current->utask->vaddr = slot_addr;
- offset = current->utask->xol_vaddr & ~PAGE_MASK;
+ /* Initialize the slot */
+ offset = xol_vaddr & ~PAGE_MASK;
vaddr = kmap_atomic(area->page);
memcpy(vaddr + offset, uprobe->arch.insn, MAX_UINSN_BYTES);
kunmap_atomic(vaddr);
@@ -1209,7 +1205,7 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot
*/
flush_dcache_page(area->page);

- return current->utask->xol_vaddr;
+ return xol_vaddr;
}

/*
@@ -1306,12 +1302,21 @@ static struct uprobe_task *get_utask(void)

/* Prepare to single-step probed instruction out of line. */
static int
-pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long vaddr)
+pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
{
- if (xol_get_insn_slot(uprobe, vaddr) && !arch_uprobe_pre_xol(&uprobe->arch, regs))
- return 0;
+ struct uprobe_task *utask;
+ unsigned long xol_vaddr;
+
+ utask = current->utask;
+
+ xol_vaddr = xol_get_insn_slot(uprobe);
+ if (!xol_vaddr)
+ return -ENOMEM;
+
+ utask->xol_vaddr = xol_vaddr;
+ utask->vaddr = bp_vaddr;

- return -EFAULT;
+ return arch_uprobe_pre_xol(&uprobe->arch, regs);
}

/*
--
1.5.5.1


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