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
proc.c
// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Scatterlist Cryptographic API.
*
* Procfs information.
*
* Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
* Copyright (c) 2005 Herbert Xu <herbert@gondor.apana.org.au>
*/
#include <linux/atomic.h>
#include <linux/init.h>
#include <linux/crypto.h>
#include <linux/module.h> /* for module_name() */
#include <linux/rwsem.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include "internal.h"
static void *c_start(struct seq_file *m, loff_t *pos)
{
down_read(&crypto_alg_sem);
return seq_list_start(&crypto_alg_list, *pos);
}
static void *c_next(struct seq_file *m, void *p, loff_t *pos)
{
return seq_list_next(p, &crypto_alg_list, pos);
}
static void c_stop(struct seq_file *m, void *p)
{
up_read(&crypto_alg_sem);
}
static int c_show(struct seq_file *m, void *p)
{
struct crypto_alg *alg = list_entry(p, struct crypto_alg, cra_list);
seq_printf(m, "name : %s\n", alg->cra_name);
seq_printf(m, "driver : %s\n", alg->cra_driver_name);
seq_printf(m, "module : %s\n", module_name(alg->cra_module));
seq_printf(m, "priority : %d\n", alg->cra_priority);
seq_printf(m, "refcnt : %u\n", refcount_read(&alg->cra_refcnt));
seq_printf(m, "selftest : %s\n",
(alg->cra_flags & CRYPTO_ALG_TESTED) ?
"passed" : "unknown");
seq_printf(m, "internal : %s\n",
(alg->cra_flags & CRYPTO_ALG_INTERNAL) ?
"yes" : "no");
if (alg->cra_flags & CRYPTO_ALG_LARVAL) {
seq_printf(m, "type : larval\n");
seq_printf(m, "flags : 0x%x\n", alg->cra_flags);
goto out;
}
if (alg->cra_type && alg->cra_type->show) {
alg->cra_type->show(m, alg);
goto out;
}
switch (alg->cra_flags & CRYPTO_ALG_TYPE_MASK) {
case CRYPTO_ALG_TYPE_CIPHER:
seq_printf(m, "type : cipher\n");
seq_printf(m, "blocksize : %u\n", alg->cra_blocksize);
seq_printf(m, "min keysize : %u\n",
alg->cra_cipher.cia_min_keysize);
seq_printf(m, "max keysize : %u\n",
alg->cra_cipher.cia_max_keysize);
break;
case CRYPTO_ALG_TYPE_COMPRESS:
seq_printf(m, "type : compression\n");
break;
default:
seq_printf(m, "type : unknown\n");
break;
}
out:
seq_putc(m, '\n');
return 0;
}
static const struct seq_operations crypto_seq_ops = {
.start = c_start,
.next = c_next,
.stop = c_stop,
.show = c_show
};
void __init crypto_init_proc(void)
{
proc_create_seq("crypto", 0, NULL, &crypto_seq_ops);
}
void __exit crypto_exit_proc(void)
{
remove_proc_entry("crypto", NULL);
}
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