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SubjectRe: [PATCH 09/14] arm64: kexec_file: add sha256 digest check in purgatory
On 24 August 2017 at 09:18, AKASHI Takahiro <takahiro.akashi@linaro.org> wrote:
> Most of sha256 code is based on crypto/sha256-glue.c, particularly using
> non-neon version.
>
> Please note that we won't be able to re-use lib/mem*.S for purgatory
> because unaligned memory access is not allowed in purgatory where mmu
> is turned off.
>
> Since purgatory is not linked with the other part of kernel, care must be
> taken of selecting an appropriate set of compiler options in order to
> prevent undefined symbol references from being generated.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> arch/arm64/crypto/sha256-core.S_shipped | 2 +
> arch/arm64/purgatory/Makefile | 21 ++++++++-
> arch/arm64/purgatory/entry.S | 13 ++++++
> arch/arm64/purgatory/purgatory.c | 20 +++++++++
> arch/arm64/purgatory/sha256-core.S | 1 +
> arch/arm64/purgatory/sha256.c | 79 +++++++++++++++++++++++++++++++++
> arch/arm64/purgatory/sha256.h | 1 +
> arch/arm64/purgatory/string.c | 32 +++++++++++++
> arch/arm64/purgatory/string.h | 5 +++
> 9 files changed, 173 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/purgatory/purgatory.c
> create mode 100644 arch/arm64/purgatory/sha256-core.S
> create mode 100644 arch/arm64/purgatory/sha256.c
> create mode 100644 arch/arm64/purgatory/sha256.h
> create mode 100644 arch/arm64/purgatory/string.c
> create mode 100644 arch/arm64/purgatory/string.h
>
> diff --git a/arch/arm64/crypto/sha256-core.S_shipped b/arch/arm64/crypto/sha256-core.S_shipped
> index 3ce82cc860bc..9ce7419c9152 100644
> --- a/arch/arm64/crypto/sha256-core.S_shipped
> +++ b/arch/arm64/crypto/sha256-core.S_shipped
> @@ -1210,6 +1210,7 @@ sha256_block_armv8:
> ret
> .size sha256_block_armv8,.-sha256_block_armv8
> #endif
> +#ifndef __PURGATORY__
> #ifdef __KERNEL__
> .globl sha256_block_neon
> #endif
> @@ -2056,6 +2057,7 @@ sha256_block_neon:
> add sp,sp,#16*4+16
> ret
> .size sha256_block_neon,.-sha256_block_neon
> +#endif
> #ifndef __KERNEL__
> .comm OPENSSL_armcap_P,4,4
> #endif

Could you please try to find another way to address this?
sha256-core.S_shipped is generated code from the accompanying Perl
script, and that script is kept in sync with upstream OpenSSL. Also,
the performance delta between the generic code is not /that/
spectacular, so we may simply use that instead.


> diff --git a/arch/arm64/purgatory/Makefile b/arch/arm64/purgatory/Makefile
> index c2127a2cbd51..d9b38be31e0a 100644
> --- a/arch/arm64/purgatory/Makefile
> +++ b/arch/arm64/purgatory/Makefile
> @@ -1,14 +1,33 @@
> OBJECT_FILES_NON_STANDARD := y
>
> -purgatory-y := entry.o
> +purgatory-y := entry.o purgatory.o sha256.o sha256-core.o string.o
>
> targets += $(purgatory-y)
> PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
>
> +# Purgatory is expected to be ET_REL, not an executable
> LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined \
> -nostdlib -z nodefaultlib
> +
> targets += purgatory.ro
>
> +GCOV_PROFILE := n
> +KASAN_SANITIZE := n
> +KCOV_INSTRUMENT := n
> +
> +# Some kernel configurations may generate additional code containing
> +# undefined symbols, like _mcount for ftrace and __stack_chk_guard
> +# for stack-protector. Those should be removed from purgatory.
> +
> +CFLAGS_REMOVE_purgatory.o = -pg
> +CFLAGS_REMOVE_sha256.o = -pg
> +CFLAGS_REMOVE_string.o = -pg
> +
> +NO_PROTECTOR := $(call cc-option, -fno-stack-protector)
> +KBUILD_CFLAGS += $(NO_PROTECTOR)
> +
> +KBUILD_AFLAGS += -D__PURGATORY__
> +
> $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
> $(call if_changed,ld)
>
> diff --git a/arch/arm64/purgatory/entry.S b/arch/arm64/purgatory/entry.S
> index bc4e6b3bf8a1..74d028b838bd 100644
> --- a/arch/arm64/purgatory/entry.S
> +++ b/arch/arm64/purgatory/entry.S
> @@ -6,6 +6,11 @@
> .text
>
> ENTRY(purgatory_start)
> + adr x19, .Lstack
> + mov sp, x19
> +
> + bl purgatory
> +
> /* Start new image. */
> ldr x17, arm64_kernel_entry
> ldr x0, arm64_dtb_addr
> @@ -15,6 +20,14 @@ ENTRY(purgatory_start)
> br x17
> END(purgatory_start)
>
> +.ltorg
> +
> +.align 4
> + .rept 256
> + .quad 0
> + .endr
> +.Lstack:
> +
> .data
>
> .align 3
> diff --git a/arch/arm64/purgatory/purgatory.c b/arch/arm64/purgatory/purgatory.c
> new file mode 100644
> index 000000000000..7fcbefa786bc
> --- /dev/null
> +++ b/arch/arm64/purgatory/purgatory.c
> @@ -0,0 +1,20 @@
> +/*
> + * purgatory: Runs between two kernels
> + *
> + * Copyright (c) 2017 Linaro Limited
> + * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
> + */
> +
> +#include "sha256.h"
> +
> +void purgatory(void)
> +{
> + int ret;
> +
> + ret = verify_sha256_digest();
> + if (ret) {
> + /* loop forever */
> + for (;;)
> + ;
> + }
> +}
> diff --git a/arch/arm64/purgatory/sha256-core.S b/arch/arm64/purgatory/sha256-core.S
> new file mode 100644
> index 000000000000..24f5ce25b61e
> --- /dev/null
> +++ b/arch/arm64/purgatory/sha256-core.S
> @@ -0,0 +1 @@
> +#include "../crypto/sha256-core.S_shipped"
> diff --git a/arch/arm64/purgatory/sha256.c b/arch/arm64/purgatory/sha256.c
> new file mode 100644
> index 000000000000..5d20d81767e3
> --- /dev/null
> +++ b/arch/arm64/purgatory/sha256.c
> @@ -0,0 +1,79 @@
> +#include <linux/kexec.h>
> +#include <linux/purgatory.h>
> +#include <linux/types.h>
> +
> +/*
> + * Under KASAN, those are defined as un-instrumented version, __memxxx()
> + */
> +#undef memcmp
> +#undef memcpy
> +#undef memset
> +
> +#include "string.h"
> +#include <crypto/hash.h>
> +#include <crypto/sha.h>
> +#include <crypto/sha256_base.h>
> +
> +u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE] __section(.kexec-purgatory);
> +struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX]
> + __section(.kexec-purgatory);
> +
> +asmlinkage void sha256_block_data_order(u32 *digest, const void *data,
> + unsigned int num_blks);
> +
> +static int sha256_init(struct shash_desc *desc)
> +{
> + return sha256_base_init(desc);
> +}
> +
> +static int sha256_update(struct shash_desc *desc, const u8 *data,
> + unsigned int len)
> +{
> + return sha256_base_do_update(desc, data, len,
> + (sha256_block_fn *)sha256_block_data_order);
> +}
> +
> +static int __sha256_base_finish(struct shash_desc *desc, u8 *out)
> +{
> + /* we can't do crypto_shash_digestsize(desc->tfm) */
> + unsigned int digest_size = 32;
> + struct sha256_state *sctx = shash_desc_ctx(desc);
> + __be32 *digest = (__be32 *)out;
> + int i;
> +
> + for (i = 0; digest_size > 0; i++, digest_size -= sizeof(__be32))
> + put_unaligned_be32(sctx->state[i], digest++);
> +
> + *sctx = (struct sha256_state){};
> + return 0;
> +}
> +
> +static int sha256_final(struct shash_desc *desc, u8 *out)
> +{
> + sha256_base_do_finalize(desc,
> + (sha256_block_fn *)sha256_block_data_order);
> +
> + return __sha256_base_finish(desc, out);
> +}
> +
> +int verify_sha256_digest(void)
> +{
> + char __sha256_desc[sizeof(struct shash_desc) +
> + sizeof(struct sha256_state)] CRYPTO_MINALIGN_ATTR;
> + struct shash_desc *desc = (struct shash_desc *)__sha256_desc;
> + struct kexec_sha_region *ptr, *end;
> + u8 digest[SHA256_DIGEST_SIZE];
> +
> + sha256_init(desc);
> +
> + end = purgatory_sha_regions + ARRAY_SIZE(purgatory_sha_regions);
> + for (ptr = purgatory_sha_regions; ptr < end; ptr++)
> + sha256_update(desc, (uint8_t *)(ptr->start), ptr->len);
> +
> + sha256_final(desc, digest);
> +
> + if (memcmp(digest, purgatory_sha256_digest, sizeof(digest)))
> + return 1;
> +
> + return 0;
> +}
> diff --git a/arch/arm64/purgatory/sha256.h b/arch/arm64/purgatory/sha256.h
> new file mode 100644
> index 000000000000..54dc3c33c469
> --- /dev/null
> +++ b/arch/arm64/purgatory/sha256.h
> @@ -0,0 +1 @@
> +extern int verify_sha256_digest(void);
> diff --git a/arch/arm64/purgatory/string.c b/arch/arm64/purgatory/string.c
> new file mode 100644
> index 000000000000..33233a210a65
> --- /dev/null
> +++ b/arch/arm64/purgatory/string.c
> @@ -0,0 +1,32 @@
> +#include <linux/types.h>
> +
> +void *memcpy(void *dst, const void *src, size_t len)
> +{
> + int i;
> +
> + for (i = 0; i < len; i++)
> + ((u8 *)dst)[i] = ((u8 *)src)[i];
> +
> + return NULL;
> +}
> +
> +void *memset(void *dst, int c, size_t len)
> +{
> + int i;
> +
> + for (i = 0; i < len; i++)
> + ((u8 *)dst)[i] = (u8)c;
> +
> + return NULL;
> +}
> +
> +int memcmp(const void *src, const void *dst, size_t len)
> +{
> + int i;
> +
> + for (i = 0; i < len; i++)
> + if (*(char *)src != *(char *)dst)
> + return 1;
> +
> + return 0;
> +}
> diff --git a/arch/arm64/purgatory/string.h b/arch/arm64/purgatory/string.h
> new file mode 100644
> index 000000000000..cb5f68dd84ef
> --- /dev/null
> +++ b/arch/arm64/purgatory/string.h
> @@ -0,0 +1,5 @@
> +#include <linux/types.h>
> +
> +int memcmp(const void *s1, const void *s2, size_t len);
> +void *memcpy(void *dst, const void *src, size_t len);
> +void *memset(void *dst, int c, size_t len);
> --
> 2.14.1
>

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