[PATCH 4.19 96/99] x86/mm: Fix a crash with kmemleak_scan()

From: Greg Kroah-Hartman
Date: Mon May 06 2019 - 10:44:13 EST

From: Qian Cai <cai@xxxxxx>

commit 0d02113b31b2017dd349ec9df2314e798a90fa6e upstream.

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


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

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:

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@xxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190423165811.36699-1-cai@xxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/x86/mm/init.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -6,6 +6,7 @@
#include <linux/bootmem.h> /* for max_low_pfn */
#include <linux/swapfile.h>
#include <linux/swapops.h>
+#include <linux/kmemleak.h>

#include <asm/set_memory.h>
#include <asm/e820/api.h>
@@ -767,6 +768,11 @@ void free_init_pages(char *what, unsigne
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 {