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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
1 parent da3bb20
Raw File
xxhash_generic.c 
// SPDX-License-Identifier: GPL-2.0

#include <crypto/internal/hash.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/xxhash.h>
#include <asm/unaligned.h>

#define XXHASH64_BLOCK_SIZE	32
#define XXHASH64_DIGEST_SIZE	8

struct xxhash64_tfm_ctx {
	u64 seed;
};

struct xxhash64_desc_ctx {
	struct xxh64_state xxhstate;
};

static int xxhash64_setkey(struct crypto_shash *tfm, const u8 *key,
			 unsigned int keylen)
{
	struct xxhash64_tfm_ctx *tctx = crypto_shash_ctx(tfm);

	if (keylen != sizeof(tctx->seed))
		return -EINVAL;
	tctx->seed = get_unaligned_le64(key);
	return 0;
}

static int xxhash64_init(struct shash_desc *desc)
{
	struct xxhash64_tfm_ctx *tctx = crypto_shash_ctx(desc->tfm);
	struct xxhash64_desc_ctx *dctx = shash_desc_ctx(desc);

	xxh64_reset(&dctx->xxhstate, tctx->seed);

	return 0;
}

static int xxhash64_update(struct shash_desc *desc, const u8 *data,
			 unsigned int length)
{
	struct xxhash64_desc_ctx *dctx = shash_desc_ctx(desc);

	xxh64_update(&dctx->xxhstate, data, length);

	return 0;
}

static int xxhash64_final(struct shash_desc *desc, u8 *out)
{
	struct xxhash64_desc_ctx *dctx = shash_desc_ctx(desc);

	put_unaligned_le64(xxh64_digest(&dctx->xxhstate), out);

	return 0;
}

static int xxhash64_digest(struct shash_desc *desc, const u8 *data,
			 unsigned int length, u8 *out)
{
	struct xxhash64_tfm_ctx *tctx = crypto_shash_ctx(desc->tfm);

	put_unaligned_le64(xxh64(data, length, tctx->seed), out);

	return 0;
}

static struct shash_alg alg = {
	.digestsize	= XXHASH64_DIGEST_SIZE,
	.setkey		= xxhash64_setkey,
	.init		= xxhash64_init,
	.update		= xxhash64_update,
	.final		= xxhash64_final,
	.digest		= xxhash64_digest,
	.descsize	= sizeof(struct xxhash64_desc_ctx),
	.base		= {
		.cra_name	 = "xxhash64",
		.cra_driver_name = "xxhash64-generic",
		.cra_priority	 = 100,
		.cra_flags	 = CRYPTO_ALG_OPTIONAL_KEY,
		.cra_blocksize	 = XXHASH64_BLOCK_SIZE,
		.cra_ctxsize	 = sizeof(struct xxhash64_tfm_ctx),
		.cra_module	 = THIS_MODULE,
	}
};

static int __init xxhash_mod_init(void)
{
	return crypto_register_shash(&alg);
}

static void __exit xxhash_mod_fini(void)
{
	crypto_unregister_shash(&alg);
}

subsys_initcall(xxhash_mod_init);
module_exit(xxhash_mod_fini);

MODULE_AUTHOR("Nikolay Borisov <nborisov@suse.com>");
MODULE_DESCRIPTION("xxhash calculations wrapper for lib/xxhash.c");
MODULE_LICENSE("GPL");
MODULE_ALIAS_CRYPTO("xxhash64");
MODULE_ALIAS_CRYPTO("xxhash64-generic");
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