linux-kernel - [PATCH 3.16 298/366] x86/kexec: Avoid double free_page() upon do_kexec

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Message-ID: <lsq.1539530741.998618943@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Thomas Gleixner" <tglx@...utronix.de>,
        thomas.lendacky@....com,
        "Tetsuo Handa" <penguin-kernel@...ove.SAKURA.ne.jp>,
        "Baoquan He" <bhe@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
        "Huang Ying" <ying.huang@...el.com>,
        kirill.shutemov@...ux.intel.com,
        "syzbot" <syzbot+d96f60296ef613fe1d69@...kaller.appspotmail.com>,
        dyoung@...hat.com, prudo@...ux.vnet.ibm.com,
        syzkaller-bugs@...glegroups.com, takahiro.akashi@...aro.org
Subject: [PATCH 3.16 298/366] x86/kexec: Avoid double free_page() upon
 do_kexec_load() failure

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

commit a466ef76b815b86748d9870ef2a430af7b39c710 upstream.

>>From ff82bedd3e12f0d3353282054ae48c3bd8c72012 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Wed, 9 May 2018 12:12:39 +0900
Subject: [PATCH v3] x86/kexec: avoid double free_page() upon do_kexec_load() failure.

syzbot is reporting crashes after memory allocation failure inside
do_kexec_load() [1]. This is because free_transition_pgtable() is called
by both init_transition_pgtable() and machine_kexec_cleanup() when memory
allocation failed inside init_transition_pgtable().

Regarding 32bit code, machine_kexec_free_page_tables() is called by both
machine_kexec_alloc_page_tables() and machine_kexec_cleanup() when memory
allocation failed inside machine_kexec_alloc_page_tables().

Fix this by leaving the error handling to machine_kexec_cleanup()
(and optionally setting NULL after free_page()).

[1] https://syzkaller.appspot.com/bug?id=91e52396168cf2bdd572fe1e1bc0bc645c1c6b40

Fixes: f5deb79679af6eb4 ("x86: kexec: Use one page table in x86_64 machine_kexec")
Fixes: 92be3d6bdf2cb349 ("kexec/i386: allocate page table pages dynamically")
Reported-by: syzbot <syzbot+d96f60296ef613fe1d69@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Baoquan He <bhe@...hat.com>
Cc: thomas.lendacky@....com
Cc: prudo@...ux.vnet.ibm.com
Cc: Huang Ying <ying.huang@...el.com>
Cc: syzkaller-bugs@...glegroups.com
Cc: takahiro.akashi@...aro.org
Cc: H. Peter Anvin <hpa@...or.com>
Cc: akpm@...ux-foundation.org
Cc: dyoung@...hat.com
Cc: kirill.shutemov@...ux.intel.com
Link: https://lkml.kernel.org/r/201805091942.DGG12448.tMFVFSJFQOOLHO@I-love.SAKURA.ne.jp
[bwh: Backported to 3.16: No need to handle a P4D]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/arch/x86/kernel/machine_kexec_32.c
+++ b/arch/x86/kernel/machine_kexec_32.c
@@ -70,12 +70,17 @@ static void load_segments(void)
 static void machine_kexec_free_page_tables(struct kimage *image)
 {
 	free_page((unsigned long)image->arch.pgd);
+	image->arch.pgd = NULL;
 #ifdef CONFIG_X86_PAE
 	free_page((unsigned long)image->arch.pmd0);
+	image->arch.pmd0 = NULL;
 	free_page((unsigned long)image->arch.pmd1);
+	image->arch.pmd1 = NULL;
 #endif
 	free_page((unsigned long)image->arch.pte0);
+	image->arch.pte0 = NULL;
 	free_page((unsigned long)image->arch.pte1);
+	image->arch.pte1 = NULL;
 }
 
 static int machine_kexec_alloc_page_tables(struct kimage *image)
@@ -92,7 +97,6 @@ static int machine_kexec_alloc_page_tabl
 	    !image->arch.pmd0 || !image->arch.pmd1 ||
 #endif
 	    !image->arch.pte0 || !image->arch.pte1) {
-		machine_kexec_free_page_tables(image);
 		return -ENOMEM;
 	}
 	return 0;
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -25,8 +25,11 @@
 static void free_transition_pgtable(struct kimage *image)
 {
 	free_page((unsigned long)image->arch.pud);
+	image->arch.pud = NULL;
 	free_page((unsigned long)image->arch.pmd);
+	image->arch.pmd = NULL;
 	free_page((unsigned long)image->arch.pte);
+	image->arch.pte = NULL;
 }
 
 static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
@@ -67,7 +70,6 @@ static int init_transition_pgtable(struc
 	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC));
 	return 0;
 err:
-	free_transition_pgtable(image);
 	return result;
 }