Revision 8ec7791bae1327b1c279c5cd6e929c3b12daaf0a authored by Michael Ellerman on 06 May 2021, 04:49:58 UTC, committed by Michael Ellerman on 14 May 2021, 07:27:36 UTC
The STF (store-to-load forwarding) barrier mitigation can be
enabled/disabled at runtime via a debugfs file (stf_barrier), which
causes the kernel to patch itself to enable/disable the relevant
mitigations.
However depending on which mitigation we're using, it may not be safe to
do that patching while other CPUs are active. For example the following
crash:
User access of kernel address (c00000003fff5af0) - exploit attempt? (uid: 0)
segfault (11) at c00000003fff5af0 nip 7fff8ad12198 lr 7fff8ad121f8 code 1
code: 40820128 e93c00d0 e9290058 7c292840 40810058 38600000 4bfd9a81 e8410018
code: 2c030006 41810154 3860ffb6 e9210098 <e94d8ff0> 7d295279 39400000 40820a3c
Shows that we returned to userspace without restoring the user r13
value, due to executing the partially patched STF exit code.
Fix it by doing the patching under stop machine. The CPUs that aren't
doing the patching will be spinning in the core of the stop machine
logic. That is currently sufficient for our purposes, because none of
the patching we do is to that code or anywhere in the vicinity.
Fixes: a048a07d7f45 ("powerpc/64s: Add support for a store forwarding barrier at kernel entry/exit")
Cc: stable@vger.kernel.org # v4.17+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210506044959.1298123-1-mpe@ellerman.id.au
1 parent da3bb20
pcbc.c
// SPDX-License-Identifier: GPL-2.0-or-later
/*
* PCBC: Propagating Cipher Block Chaining mode
*
* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* Derived from cbc.c
* - Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
*/
#include <crypto/algapi.h>
#include <crypto/internal/cipher.h>
#include <crypto/internal/skcipher.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
static int crypto_pcbc_encrypt_segment(struct skcipher_request *req,
struct skcipher_walk *walk,
struct crypto_cipher *tfm)
{
int bsize = crypto_cipher_blocksize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 * const iv = walk->iv;
do {
crypto_xor(iv, src, bsize);
crypto_cipher_encrypt_one(tfm, dst, iv);
crypto_xor_cpy(iv, dst, src, bsize);
src += bsize;
dst += bsize;
} while ((nbytes -= bsize) >= bsize);
return nbytes;
}
static int crypto_pcbc_encrypt_inplace(struct skcipher_request *req,
struct skcipher_walk *walk,
struct crypto_cipher *tfm)
{
int bsize = crypto_cipher_blocksize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 * const iv = walk->iv;
u8 tmpbuf[MAX_CIPHER_BLOCKSIZE];
do {
memcpy(tmpbuf, src, bsize);
crypto_xor(iv, src, bsize);
crypto_cipher_encrypt_one(tfm, src, iv);
crypto_xor_cpy(iv, tmpbuf, src, bsize);
src += bsize;
} while ((nbytes -= bsize) >= bsize);
return nbytes;
}
static int crypto_pcbc_encrypt(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
struct skcipher_walk walk;
unsigned int nbytes;
int err;
err = skcipher_walk_virt(&walk, req, false);
while ((nbytes = walk.nbytes)) {
if (walk.src.virt.addr == walk.dst.virt.addr)
nbytes = crypto_pcbc_encrypt_inplace(req, &walk,
cipher);
else
nbytes = crypto_pcbc_encrypt_segment(req, &walk,
cipher);
err = skcipher_walk_done(&walk, nbytes);
}
return err;
}
static int crypto_pcbc_decrypt_segment(struct skcipher_request *req,
struct skcipher_walk *walk,
struct crypto_cipher *tfm)
{
int bsize = crypto_cipher_blocksize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 * const iv = walk->iv;
do {
crypto_cipher_decrypt_one(tfm, dst, src);
crypto_xor(dst, iv, bsize);
crypto_xor_cpy(iv, dst, src, bsize);
src += bsize;
dst += bsize;
} while ((nbytes -= bsize) >= bsize);
return nbytes;
}
static int crypto_pcbc_decrypt_inplace(struct skcipher_request *req,
struct skcipher_walk *walk,
struct crypto_cipher *tfm)
{
int bsize = crypto_cipher_blocksize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 * const iv = walk->iv;
u8 tmpbuf[MAX_CIPHER_BLOCKSIZE] __aligned(__alignof__(u32));
do {
memcpy(tmpbuf, src, bsize);
crypto_cipher_decrypt_one(tfm, src, src);
crypto_xor(src, iv, bsize);
crypto_xor_cpy(iv, src, tmpbuf, bsize);
src += bsize;
} while ((nbytes -= bsize) >= bsize);
return nbytes;
}
static int crypto_pcbc_decrypt(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
struct skcipher_walk walk;
unsigned int nbytes;
int err;
err = skcipher_walk_virt(&walk, req, false);
while ((nbytes = walk.nbytes)) {
if (walk.src.virt.addr == walk.dst.virt.addr)
nbytes = crypto_pcbc_decrypt_inplace(req, &walk,
cipher);
else
nbytes = crypto_pcbc_decrypt_segment(req, &walk,
cipher);
err = skcipher_walk_done(&walk, nbytes);
}
return err;
}
static int crypto_pcbc_create(struct crypto_template *tmpl, struct rtattr **tb)
{
struct skcipher_instance *inst;
int err;
inst = skcipher_alloc_instance_simple(tmpl, tb);
if (IS_ERR(inst))
return PTR_ERR(inst);
inst->alg.encrypt = crypto_pcbc_encrypt;
inst->alg.decrypt = crypto_pcbc_decrypt;
err = skcipher_register_instance(tmpl, inst);
if (err)
inst->free(inst);
return err;
}
static struct crypto_template crypto_pcbc_tmpl = {
.name = "pcbc",
.create = crypto_pcbc_create,
.module = THIS_MODULE,
};
static int __init crypto_pcbc_module_init(void)
{
return crypto_register_template(&crypto_pcbc_tmpl);
}
static void __exit crypto_pcbc_module_exit(void)
{
crypto_unregister_template(&crypto_pcbc_tmpl);
}
subsys_initcall(crypto_pcbc_module_init);
module_exit(crypto_pcbc_module_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("PCBC block cipher mode of operation");
MODULE_ALIAS_CRYPTO("pcbc");
MODULE_IMPORT_NS(CRYPTO_INTERNAL);
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