Re: [PATCH 09/14] arm64: kexec_file: add sha256 digest check in purgatory

[Ard Biesheuvel]

On 24 August 2017 at 09:18, AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> 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@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>
> + */
> +
> +#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
>