linux-kernel - [PATCH 4.19 96/99] x86/mm: Fix a crash with kmemleak

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Message-Id: <20190506143102.536637385@linuxfoundation.org>
Date:   Mon,  6 May 2019 16:33:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Qian Cai <cai@....pw>,
        Borislav Petkov <bp@...e.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Brijesh Singh <brijesh.singh@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>
Subject: [PATCH 4.19 96/99] x86/mm: Fix a crash with kmemleak_scan()

From: Qian Cai <cai@....pw>

commit 0d02113b31b2017dd349ec9df2314e798a90fa6e upstream.

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@....pw>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Brijesh Singh <brijesh.singh@....com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/20190423165811.36699-1-cai@lca.pw
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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 {
 		/*