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
tpm_parser.c
// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) "TPM-PARSER: "fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <keys/asymmetric-subtype.h>
#include <keys/asymmetric-parser.h>
#include <crypto/asym_tpm_subtype.h>
#include "tpm.asn1.h"
struct tpm_parse_context {
const void *blob;
u32 blob_len;
};
/*
* Note the key data of the ASN.1 blob.
*/
int tpm_note_key(void *context, size_t hdrlen,
unsigned char tag,
const void *value, size_t vlen)
{
struct tpm_parse_context *ctx = context;
ctx->blob = value;
ctx->blob_len = vlen;
return 0;
}
/*
* Parse a TPM-encrypted private key blob.
*/
static struct tpm_key *tpm_parse(const void *data, size_t datalen)
{
struct tpm_parse_context ctx;
long ret;
memset(&ctx, 0, sizeof(ctx));
/* Attempt to decode the private key */
ret = asn1_ber_decoder(&tpm_decoder, &ctx, data, datalen);
if (ret < 0)
goto error;
return tpm_key_create(ctx.blob, ctx.blob_len);
error:
return ERR_PTR(ret);
}
/*
* Attempt to parse a data blob for a key as a TPM private key blob.
*/
static int tpm_key_preparse(struct key_preparsed_payload *prep)
{
struct tpm_key *tk;
/*
* TPM 1.2 keys are max 2048 bits long, so assume the blob is no
* more than 4x that
*/
if (prep->datalen > 256 * 4)
return -EMSGSIZE;
tk = tpm_parse(prep->data, prep->datalen);
if (IS_ERR(tk))
return PTR_ERR(tk);
/* We're pinning the module by being linked against it */
__module_get(asym_tpm_subtype.owner);
prep->payload.data[asym_subtype] = &asym_tpm_subtype;
prep->payload.data[asym_key_ids] = NULL;
prep->payload.data[asym_crypto] = tk;
prep->payload.data[asym_auth] = NULL;
prep->quotalen = 100;
return 0;
}
static struct asymmetric_key_parser tpm_key_parser = {
.owner = THIS_MODULE,
.name = "tpm_parser",
.parse = tpm_key_preparse,
};
static int __init tpm_key_init(void)
{
return register_asymmetric_key_parser(&tpm_key_parser);
}
static void __exit tpm_key_exit(void)
{
unregister_asymmetric_key_parser(&tpm_key_parser);
}
module_init(tpm_key_init);
module_exit(tpm_key_exit);
MODULE_DESCRIPTION("TPM private key-blob parser");
MODULE_LICENSE("GPL v2");
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