linux-kernel - [tip:perf/core] uprobes: Fix the usage of install_special

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Message-ID: <tip-f58bea2fec63db72f8050ade709358257e9102ab@git.kernel.org>
Date:	Fri, 31 Jul 2015 07:01:26 -0700
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, luto@...capital.net,
	tglx@...utronix.de, mingo@...nel.org, srikar@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org, hpa@...or.com, oleg@...hat.com,
	peterz@...radead.org, panand@...hat.com
Subject: [tip:perf/core] uprobes: Fix the usage of install_special_mapping
 ()

Commit-ID:  f58bea2fec63db72f8050ade709358257e9102ab
Gitweb:     http://git.kernel.org/tip/f58bea2fec63db72f8050ade709358257e9102ab
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Tue, 21 Jul 2015 15:40:31 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 31 Jul 2015 10:38:06 +0200

uprobes: Fix the usage of install_special_mapping()

install_special_mapping(pages) expects that "pages" is the zero-
terminated array while xol_add_vma() passes &area->page, this
means that special_mapping_fault() can wrongly use the next
member in xol_area (vaddr) as "struct page *".

Fortunately, this area is not expandable so pgoff != 0 isn't
possible (modulo bugs in special_mapping_vmops), but still this
does not look good.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Pratyush Anand <panand@...hat.com>
Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20150721134031.GA4789@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/uprobes.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 0f370ef..4b8ac5f 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -99,7 +99,7 @@ struct xol_area {
 	wait_queue_head_t 	wq;		/* if all slots are busy */
 	atomic_t 		slot_count;	/* number of in-use slots */
 	unsigned long 		*bitmap;	/* 0 = free slot */
-	struct page 		*page;
+	struct page 		*pages[2];
 
 	/*
 	 * We keep the vma's vm_start rather than a pointer to the vma
@@ -1142,7 +1142,7 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
 	}
 
 	ret = install_special_mapping(mm, area->vaddr, PAGE_SIZE,
-				VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO, &area->page);
+				VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO, area->pages);
 	if (ret)
 		goto fail;
 
@@ -1168,21 +1168,22 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
 	if (!area->bitmap)
 		goto free_area;
 
-	area->page = alloc_page(GFP_HIGHUSER);
-	if (!area->page)
+	area->pages[0] = alloc_page(GFP_HIGHUSER);
+	if (!area->pages[0])
 		goto free_bitmap;
+	area->pages[1] = NULL;
 
 	area->vaddr = vaddr;
 	init_waitqueue_head(&area->wq);
 	/* Reserve the 1st slot for get_trampoline_vaddr() */
 	set_bit(0, area->bitmap);
 	atomic_set(&area->slot_count, 1);
-	copy_to_page(area->page, 0, &insn, UPROBE_SWBP_INSN_SIZE);
+	copy_to_page(area->pages[0], 0, &insn, UPROBE_SWBP_INSN_SIZE);
 
 	if (!xol_add_vma(mm, area))
 		return area;
 
-	__free_page(area->page);
+	__free_page(area->pages[0]);
  free_bitmap:
 	kfree(area->bitmap);
  free_area:
@@ -1220,7 +1221,7 @@ void uprobe_clear_state(struct mm_struct *mm)
 	if (!area)
 		return;
 
-	put_page(area->page);
+	put_page(area->pages[0]);
 	kfree(area->bitmap);
 	kfree(area);
 }
@@ -1289,7 +1290,7 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
 	if (unlikely(!xol_vaddr))
 		return 0;
 
-	arch_uprobe_copy_ixol(area->page, xol_vaddr,
+	arch_uprobe_copy_ixol(area->pages[0], xol_vaddr,
 			      &uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
 
 	return xol_vaddr;
--
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