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Revision eecc1e426d681351a6026a7d3e7d225f38955b6c authored by Hugh Dickins on 12 January 2014, 09:25:21 UTC, committed by Linus Torvalds on 12 January 2014, 09:47:15 UTC 
thp: fix copy_page_rep GPF by testing is_huge_zero_pmd once only
 
We see General Protection Fault on RSI in copy_page_rep: that RSI is
what you get from a NULL struct page pointer.

  RIP: 0010:[<ffffffff81154955>]  [<ffffffff81154955>] copy_page_rep+0x5/0x10
  RSP: 0000:ffff880136e15c00  EFLAGS: 00010286
  RAX: ffff880000000000 RBX: ffff880136e14000 RCX: 0000000000000200
  RDX: 6db6db6db6db6db7 RSI: db73880000000000 RDI: ffff880dd0c00000
  RBP: ffff880136e15c18 R08: 0000000000000200 R09: 000000000005987c
  R10: 000000000005987c R11: 0000000000000200 R12: 0000000000000001
  R13: ffffea00305aa000 R14: 0000000000000000 R15: 0000000000000000
  FS:  00007f195752f700(0000) GS:ffff880c7fc20000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000093010000 CR3: 00000001458e1000 CR4: 00000000000027e0
  Call Trace:
    copy_user_huge_page+0x93/0xab
    do_huge_pmd_wp_page+0x710/0x815
    handle_mm_fault+0x15d8/0x1d70
    __do_page_fault+0x14d/0x840
    do_page_fault+0x2f/0x90
    page_fault+0x22/0x30

do_huge_pmd_wp_page() tests is_huge_zero_pmd(orig_pmd) four times: but
since shrink_huge_zero_page() can free the huge_zero_page, and we have
no hold of our own on it here (except where the fourth test holds
page_table_lock and has checked pmd_same), it's possible for it to
answer yes the first time, but no to the second or third test.  Change
all those last three to tests for NULL page.

(Note: this is not the same issue as trinity's DEBUG_PAGEALLOC BUG
in copy_page_rep with RSI: ffff88009c422000, reported by Sasha Levin
in https://lkml.org/lkml/2013/3/29/103.  I believe that one is due
to the source page being split, and a tail page freed, while copy
is in progress; and not a problem without DEBUG_PAGEALLOC, since
the pmd_same check will prevent a miscopy from being made visible.)

Fixes: 97ae17497e99 ("thp: implement refcounting for huge zero page")
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: stable@vger.kernel.org # v3.10 v3.11 v3.12
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 518d00b
Raw File
krng.c 
/*
 * RNG implementation using standard kernel RNG.
 *
 * Copyright (c) 2008 Herbert Xu <herbert@gondor.apana.org.au>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * any later version.
 *
 */

#include <crypto/internal/rng.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/random.h>

static int krng_get_random(struct crypto_rng *tfm, u8 *rdata, unsigned int dlen)
{
	get_random_bytes(rdata, dlen);
	return 0;
}

static int krng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
{
	return 0;
}

static struct crypto_alg krng_alg = {
	.cra_name		= "stdrng",
	.cra_driver_name	= "krng",
	.cra_priority		= 200,
	.cra_flags		= CRYPTO_ALG_TYPE_RNG,
	.cra_ctxsize		= 0,
	.cra_type		= &crypto_rng_type,
	.cra_module		= THIS_MODULE,
	.cra_u			= {
		.rng = {
			.rng_make_random	= krng_get_random,
			.rng_reset		= krng_reset,
			.seedsize		= 0,
		}
	}
};


/* Module initalization */
static int __init krng_mod_init(void)
{
	return crypto_register_alg(&krng_alg);
}

static void __exit krng_mod_fini(void)
{
	crypto_unregister_alg(&krng_alg);
	return;
}

module_init(krng_mod_init);
module_exit(krng_mod_fini);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Kernel Random Number Generator");
MODULE_ALIAS("stdrng");
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