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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 
powerpc/64s: Fix crashes when toggling stf barrier
 
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
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Raw File
internal.h 
/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Cryptographic API.
 *
 * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
 * Copyright (c) 2005 Herbert Xu <herbert@gondor.apana.org.au>
 */
#ifndef _CRYPTO_INTERNAL_H
#define _CRYPTO_INTERNAL_H

#include <crypto/algapi.h>
#include <linux/completion.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/notifier.h>
#include <linux/numa.h>
#include <linux/refcount.h>
#include <linux/rwsem.h>
#include <linux/sched.h>
#include <linux/types.h>

struct crypto_instance;
struct crypto_template;

struct crypto_larval {
	struct crypto_alg alg;
	struct crypto_alg *adult;
	struct completion completion;
	u32 mask;
};

extern struct list_head crypto_alg_list;
extern struct rw_semaphore crypto_alg_sem;
extern struct blocking_notifier_head crypto_chain;

#ifdef CONFIG_PROC_FS
void __init crypto_init_proc(void);
void __exit crypto_exit_proc(void);
#else
static inline void crypto_init_proc(void)
{ }
static inline void crypto_exit_proc(void)
{ }
#endif

static inline unsigned int crypto_cipher_ctxsize(struct crypto_alg *alg)
{
	return alg->cra_ctxsize;
}

static inline unsigned int crypto_compress_ctxsize(struct crypto_alg *alg)
{
	return alg->cra_ctxsize;
}

struct crypto_alg *crypto_mod_get(struct crypto_alg *alg);
struct crypto_alg *crypto_alg_mod_lookup(const char *name, u32 type, u32 mask);

struct crypto_larval *crypto_larval_alloc(const char *name, u32 type, u32 mask);
void crypto_larval_kill(struct crypto_alg *alg);
void crypto_alg_tested(const char *name, int err);

void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,
			  struct crypto_alg *nalg);
void crypto_remove_final(struct list_head *list);
void crypto_shoot_alg(struct crypto_alg *alg);
struct crypto_tfm *__crypto_alloc_tfm(struct crypto_alg *alg, u32 type,
				      u32 mask);
void *crypto_create_tfm_node(struct crypto_alg *alg,
			const struct crypto_type *frontend, int node);

static inline void *crypto_create_tfm(struct crypto_alg *alg,
			const struct crypto_type *frontend)
{
	return crypto_create_tfm_node(alg, frontend, NUMA_NO_NODE);
}

struct crypto_alg *crypto_find_alg(const char *alg_name,
				   const struct crypto_type *frontend,
				   u32 type, u32 mask);

void *crypto_alloc_tfm_node(const char *alg_name,
		       const struct crypto_type *frontend, u32 type, u32 mask,
		       int node);

static inline void *crypto_alloc_tfm(const char *alg_name,
		       const struct crypto_type *frontend, u32 type, u32 mask)
{
	return crypto_alloc_tfm_node(alg_name, frontend, type, mask, NUMA_NO_NODE);
}

int crypto_probing_notify(unsigned long val, void *v);

unsigned int crypto_alg_extsize(struct crypto_alg *alg);

int crypto_type_has_alg(const char *name, const struct crypto_type *frontend,
			u32 type, u32 mask);

static inline struct crypto_alg *crypto_alg_get(struct crypto_alg *alg)
{
	refcount_inc(&alg->cra_refcnt);
	return alg;
}

static inline void crypto_alg_put(struct crypto_alg *alg)
{
	if (refcount_dec_and_test(&alg->cra_refcnt) && alg->cra_destroy)
		alg->cra_destroy(alg);
}

static inline int crypto_tmpl_get(struct crypto_template *tmpl)
{
	return try_module_get(tmpl->module);
}

static inline void crypto_tmpl_put(struct crypto_template *tmpl)
{
	module_put(tmpl->module);
}

static inline int crypto_is_larval(struct crypto_alg *alg)
{
	return alg->cra_flags & CRYPTO_ALG_LARVAL;
}

static inline int crypto_is_dead(struct crypto_alg *alg)
{
	return alg->cra_flags & CRYPTO_ALG_DEAD;
}

static inline int crypto_is_moribund(struct crypto_alg *alg)
{
	return alg->cra_flags & (CRYPTO_ALG_DEAD | CRYPTO_ALG_DYING);
}

static inline void crypto_notify(unsigned long val, void *v)
{
	blocking_notifier_call_chain(&crypto_chain, val, v);
}

static inline void crypto_yield(u32 flags)
{
	if (flags & CRYPTO_TFM_REQ_MAY_SLEEP)
		cond_resched();
}

#endif	/* _CRYPTO_INTERNAL_H */
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