[PATCH] x86/mm: fix a crash with kmemleak_scan()

[PATCH] x86/mm: fix a crash with kmemleak_scan()

[Qian Cai]

The first kmemleak_scan() after boot would trigger a crash below because

kernel_init
  free_initmem
    mem_encrypt_free_decrypted_mem
      free_init_pages

unmapped some memory inside the .bss with DEBUG_PAGEALLOC=y. Since
kmemleak_init() will register the .data/.bss sections (only register
.data..ro_after_init if not within .data) and then kmemleak_scan() will
scan those address and dereference them looking for pointer referencing.
If free_init_pages() free and unmap pages in those sections,
kmemleak_scan() will trigger a crash if referencing one of those
addresses.

BUG: unable to handle kernel paging request at ffffffffbd402000
CPU: 12 PID: 325 Comm: kmemleak Not tainted 5.1.0-rc4+ #4
RIP: 0010:scan_block+0x58/0x160
Call Trace:
 scan_gray_list+0x1d9/0x280
 kmemleak_scan+0x485/0xad0
 kmemleak_scan_thread+0x9f/0xc4
 kthread+0x1d2/0x1f0
 ret_from_fork+0x35/0x40

Since kmemleak_free_part() is tolerant to unknown objects (not tracked by
kmemleak), it is fine to call it from free_init_pages() even if not all
address ranges passed to this function are known to kmemleak.

Signed-off-by: Qian Cai <cai@lca.pw>
---
 arch/x86/mm/init.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index f905a2371080..8dacdb96899e 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -5,6 +5,7 @@
 #include <linux/memblock.h>
 #include <linux/swapfile.h>
 #include <linux/swapops.h>
+#include <linux/kmemleak.h>
 
 #include <asm/set_memory.h>
 #include <asm/e820/api.h>
@@ -766,6 +767,11 @@ void free_init_pages(const char *what, unsigned long begin, unsigned long end)
 	if (debug_pagealloc_enabled()) {
 		pr_info("debug: unmapping init [mem %#010lx-%#010lx]\n",
 			begin, end - 1);
+		/*
+		 * Inform kmemleak about the hole in the memory since the
+		 * corresponding pages will be unmapped.
+		 */
+		kmemleak_free_part((void *)begin, end - begin);
 		set_memory_np(begin, (end - begin) >> PAGE_SHIFT);
 	} else {
 		/*
-- 
2.20.1 (Apple Git-117)

Re: [PATCH] x86/mm: fix a crash with kmemleak_scan()

[Catalin Marinas]

On Tue, Apr 23, 2019 at 12:58:11PM -0400, Qian Cai wrote:
> The first kmemleak_scan() after boot would trigger a crash below because
> 
> kernel_init
>   free_initmem
>     mem_encrypt_free_decrypted_mem
>       free_init_pages
> 
> unmapped some memory inside the .bss with DEBUG_PAGEALLOC=y. Since
> kmemleak_init() will register the .data/.bss sections (only register
> .data..ro_after_init if not within .data) and then kmemleak_scan() will
> scan those address and dereference them looking for pointer referencing.
> If free_init_pages() free and unmap pages in those sections,
> kmemleak_scan() will trigger a crash if referencing one of those
> addresses.
> 
> BUG: unable to handle kernel paging request at ffffffffbd402000
> CPU: 12 PID: 325 Comm: kmemleak Not tainted 5.1.0-rc4+ #4
> RIP: 0010:scan_block+0x58/0x160
> Call Trace:
>  scan_gray_list+0x1d9/0x280
>  kmemleak_scan+0x485/0xad0
>  kmemleak_scan_thread+0x9f/0xc4
>  kthread+0x1d2/0x1f0
>  ret_from_fork+0x35/0x40
> 
> Since kmemleak_free_part() is tolerant to unknown objects (not tracked by
> kmemleak), it is fine to call it from free_init_pages() even if not all
> address ranges passed to this function are known to kmemleak.
> 
> Signed-off-by: Qian Cai <cai@lca.pw>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

[tip:x86/urgent] x86/mm: Fix a crash with kmemleak_scan()

[tip-bot for Qian Cai]

Commit-ID:  0d02113b31b2017dd349ec9df2314e798a90fa6e
Gitweb:     https://git.kernel.org/tip/0d02113b31b2017dd349ec9df2314e798a90fa6e
Author:     Qian Cai <cai@lca.pw>
AuthorDate: Tue, 23 Apr 2019 12:58:11 -0400
Committer:  Borislav Petkov <bp@suse.de>
CommitDate: Wed, 24 Apr 2019 11:32:34 +0200

x86/mm: Fix a crash with kmemleak_scan()

The first kmemleak_scan() call after boot would trigger the crash below
because this callpath:

  kernel_init
    free_initmem
      mem_encrypt_free_decrypted_mem
        free_init_pages

unmaps memory inside the .bss when DEBUG_PAGEALLOC=y.

kmemleak_init() will register the .data/.bss sections and then
kmemleak_scan() will scan those addresses and dereference them looking
for pointer references. If free_init_pages() frees and unmaps pages in
those sections, kmemleak_scan() will crash if referencing one of those
addresses:

  BUG: unable to handle kernel paging request at ffffffffbd402000
  CPU: 12 PID: 325 Comm: kmemleak Not tainted 5.1.0-rc4+ #4
  RIP: 0010:scan_block
  Call Trace:
   scan_gray_list
   kmemleak_scan
   kmemleak_scan_thread
   kthread
   ret_from_fork

Since kmemleak_free_part() is tolerant to unknown objects (not tracked
by kmemleak), it is fine to call it from free_init_pages() even if not
all address ranges passed to this function are known to kmemleak.

 [ bp: Massage. ]

Fixes: b3f0907c71e0 ("x86/mm: Add .bss..decrypted section to hold shared variables")
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190423165811.36699-1-cai@lca.pw
---
 arch/x86/mm/init.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index f905a2371080..8dacdb96899e 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -5,6 +5,7 @@
 #include <linux/memblock.h>
 #include <linux/swapfile.h>
 #include <linux/swapops.h>
+#include <linux/kmemleak.h>
 
 #include <asm/set_memory.h>
 #include <asm/e820/api.h>
@@ -766,6 +767,11 @@ void free_init_pages(const char *what, unsigned long begin, unsigned long end)
 	if (debug_pagealloc_enabled()) {
 		pr_info("debug: unmapping init [mem %#010lx-%#010lx]\n",
 			begin, end - 1);
+		/*
+		 * Inform kmemleak about the hole in the memory since the
+		 * corresponding pages will be unmapped.
+		 */
+		kmemleak_free_part((void *)begin, end - begin);
 		set_memory_np(begin, (end - begin) >> PAGE_SHIFT);
 	} else {
 		/*