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SubjectRe: [PATCH 07/11] kexec: Create a relocatable object called purgatory
On Mon, Jan 27, 2014 at 01:57:47PM -0500, Vivek Goyal wrote:
> Create a stand alone relocatable object purgatory which runs between two
> kernels. This name, concept and some code has been taken from kexec-tools.

... and the concept probably originates from Dante's "Divine Comedy" :-P

> Idea is that this code runs after a crash and it runs in minimal environment.
> So keep it separate from rest of the kernel and in long term we will have
> to practically do no maintenance of this code.
>
> This code also has the logic to do verify sha256 hashes of various
> segments which have been loaded into memory. So first we verify that
> the kernel we are jumping to is fine and has not been corrupted and
> make progress only if checsums are verified.
>
> This code also takes care of copying some memory contents to backup region.
>
> sha256 hash related code has been taken from crypto/sha256_generic.c. I
> could not call into functions exported by sha256_generic.c directly as
> we don't link against the kernel. Purgatory is a stand alone object.
>
> Also sha256_generic.c is supposed to work with higher level crypto
> abstrations and API and there was no point in importing all that in
> purgatory. So instead of doing #include on sha256_generic.c I just
> copied relevant portions of code into arch/x86/purgatory/sha256.c. Now
> we shouldn't have to touch this code at all. Do let me know if there are
> better ways to handle it.

Ok, but what about configurable encryption algorithms? Maybe there are
people who don't want to use sha-2 and prefer something else instead.

> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

Also checkpatch:

...
total: 429 errors, 5 warnings, 1409 lines checked

> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 13b22e0..fedcd16 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -160,6 +160,11 @@ archscripts: scripts_basic
> archheaders:
> $(Q)$(MAKE) $(build)=arch/x86/syscalls all
>
> +archprepare:
> +ifeq ($(CONFIG_KEXEC),y)
> + $(Q)$(MAKE) $(build)=arch/x86/purgatory arch/x86/purgatory/kexec-purgatory.c
> +endif

I wonder if this could be put into arch/x86/boot/ and built there too...
But hpa said that already.

...

> diff --git a/arch/x86/purgatory/entry64.S b/arch/x86/purgatory/entry64.S
> new file mode 100644
> index 0000000..e405c0f
> --- /dev/null
> +++ b/arch/x86/purgatory/entry64.S
> @@ -0,0 +1,111 @@
> +/*
> + * Copyright (C) 2003,2004 Eric Biederman (ebiederm@xmission.com)
> + * Copyright (C) 2014 Red Hat Inc.
> +
> + * Author(s): Vivek Goyal <vgoyal@redhat.com>
> + *
> + * This code has been taken from kexec-tools.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation (version 2 of the License).
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

Yeah, can we drop this boilerplate gunk and refer to COPYING instead.

> + */
> +
> + .text
> + .balign 16
> + .code64
> + .globl entry64, entry64_regs
> +
> +
> +entry64:
> + /* Setup a gdt that should be preserved */
> + lgdt gdt(%rip)
> +
> + /* load the data segments */
> + movl $0x18, %eax /* data segment */
> + movl %eax, %ds
> + movl %eax, %es
> + movl %eax, %ss
> + movl %eax, %fs
> + movl %eax, %gs
> +
> + /* Setup new stack */
> + leaq stack_init(%rip), %rsp
> + pushq $0x10 /* CS */
> + leaq new_cs_exit(%rip), %rax
> + pushq %rax
> + lretq
> +new_cs_exit:
> +
> + /* Load the registers */
> + movq rax(%rip), %rax
> + movq rbx(%rip), %rbx
> + movq rcx(%rip), %rcx
> + movq rdx(%rip), %rdx
> + movq rsi(%rip), %rsi
> + movq rdi(%rip), %rdi
> + movq rsp(%rip), %rsp
> + movq rbp(%rip), %rbp
> + movq r8(%rip), %r8
> + movq r9(%rip), %r9
> + movq r10(%rip), %r10
> + movq r11(%rip), %r11
> + movq r12(%rip), %r12
> + movq r13(%rip), %r13
> + movq r14(%rip), %r14
> + movq r15(%rip), %r15

Huh, is the purpose to simply clear the arch registers here?

xor %reg,%reg

?

If so, you don't need the entry64_regs and below definitions at all.
From the looks of it, though, something's populating those regs before
we jump to rip below...

> +
> + /* Jump to the new code... */
> + jmpq *rip(%rip)
> +
> + .section ".rodata"
> + .balign 4
> +entry64_regs:
> +rax: .quad 0x00000000
> +rbx: .quad 0x00000000
> +rcx: .quad 0x00000000
> +rdx: .quad 0x00000000
> +rsi: .quad 0x00000000
> +rdi: .quad 0x00000000
> +rsp: .quad 0x00000000
> +rbp: .quad 0x00000000
> +r8: .quad 0x00000000
> +r9: .quad 0x00000000
> +r10: .quad 0x00000000
> +r11: .quad 0x00000000
> +r12: .quad 0x00000000
> +r13: .quad 0x00000000
> +r14: .quad 0x00000000
> +r15: .quad 0x00000000
> +rip: .quad 0x00000000
> + .size entry64_regs, . - entry64_regs
> +
> + /* GDT */
> + .section ".rodata"
> + .balign 16
> +gdt:
> + /* 0x00 unusable segment
> + * 0x08 unused
> + * so use them as gdt ptr
> + */
> + .word gdt_end - gdt - 1
> + .quad gdt
> + .word 0, 0, 0
> +
> + /* 0x10 4GB flat code segment */
> + .word 0xFFFF, 0x0000, 0x9A00, 0x00AF
> +
> + /* 0x18 4GB flat data segment */
> + .word 0xFFFF, 0x0000, 0x9200, 0x00CF
> +gdt_end:
> +stack: .quad 0, 0
> +stack_init:
> diff --git a/arch/x86/purgatory/purgatory.c b/arch/x86/purgatory/purgatory.c
> new file mode 100644
> index 0000000..375cfb7
> --- /dev/null
> +++ b/arch/x86/purgatory/purgatory.c
> @@ -0,0 +1,103 @@
> +/*
> + * purgatory: Runs between two kernels
> + *
> + * Copyright (C) 2013 Red Hat Inc.
> + *
> + * Author:
> + *
> + * Vivek Goyal <vgoyal@redhat.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation (version 2 of the License).
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

Ditto for the boilerplate gunk.

> + */
> +
> +#include "sha256.h"
> +
> +struct sha_region {
> + unsigned long start;
> + unsigned long len;
> +};
> +
> +unsigned long backup_dest = 0;
> +unsigned long backup_src = 0;
> +unsigned long backup_sz = 0;
> +
> +u8 sha256_digest[SHA256_DIGEST_SIZE] = { 0 };
> +
> +struct sha_region sha_regions[16] = {};
> +
> +/**
> + * memcpy - Copy one area of memory to another
> + * @dest: Where to copy to
> + * @src: Where to copy from
> + * @count: The size of the area.
> + */
> +static void *memcpy(void *dest, const void *src, unsigned long count)
> +{
> + char *tmp = dest;
> + const char *s = src;
> +
> + while (count--)
> + *tmp++ = *s++;
> + return dest;
> +}
> +
> +static int memcmp(const void *cs, const void *ct, size_t count)
> +{
> + const unsigned char *su1, *su2;
> + int res = 0;
> +
> + for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)
> + if ((res = *su1 - *su2) != 0)
> + break;
> + return res;
> +}
> +
> +static int copy_backup_region(void)
> +{
> + if (backup_dest)
> + memcpy((void *)backup_dest, (void *)backup_src, backup_sz);
> +
> + return 0;
> +}
> +
> +int verify_sha256_digest(void)
> +{
> + struct sha_region *ptr, *end;
> + u8 digest[SHA256_DIGEST_SIZE];
> + struct sha256_state sctx;
> +
> + sha256_init(&sctx);
> + end = &sha_regions[sizeof(sha_regions)/sizeof(sha_regions[0])];
> + for (ptr = sha_regions; ptr < end; ptr++)
> + sha256_update(&sctx, (uint8_t *)(ptr->start), ptr->len);
> +
> + sha256_final(&sctx, digest);
> +
> + if (memcmp(digest, sha256_digest, sizeof(digest)) != 0)
> + return 1;
> +
> + return 0;
> +}
> +
> +void purgatory(void)
> +{
> + int ret;
> +
> + ret = verify_sha256_digest();

Yeah, again, hardcoding sha256 is kinda jucky. We probably should link
the needed crypto API stuff stuff and support multiple encryption algos.

> + if (ret) {
> + /* loop forever */
> + for(;;);
> + }
> + copy_backup_region();

What is this thing supposed to do? I see in patch 11/11
arch_update_purgatory() does some preparations for KEXEC_TYPE_CRASH.

> +}
> diff --git a/arch/x86/purgatory/setup-x86_32.S b/arch/x86/purgatory/setup-x86_32.S
> new file mode 100644
> index 0000000..a9d5aa5
> --- /dev/null
> +++ b/arch/x86/purgatory/setup-x86_32.S
> @@ -0,0 +1,29 @@
> +/*
> + * purgatory: setup code
> + *
> + * Copyright (C) 2014 Red Hat Inc.
> + *
> + * This code has been taken from kexec-tools.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation (version 2 of the License).
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.


Ditto on the boilerplate.

> + */
> +
> + .text
> + .globl purgatory_start
> + .balign 16
> +purgatory_start:
> + .code32
> +
> + /* This is just a stub. Write code when 32bit support comes along */

I'm guessing we want to support 32-bit secure boot with kexec at some
point...

> + call purgatory
> diff --git a/arch/x86/purgatory/setup-x86_64.S b/arch/x86/purgatory/setup-x86_64.S
> new file mode 100644
> index 0000000..d23bc54
> --- /dev/null
> +++ b/arch/x86/purgatory/setup-x86_64.S
> @@ -0,0 +1,68 @@
> +/*
> + * purgatory: setup code
> + *
> + * Copyright (C) 2003,2004 Eric Biederman (ebiederm@xmission.com)
> + * Copyright (C) 2014 Red Hat Inc.
> + *
> + * This code has been taken from kexec-tools.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation (version 2 of the License).
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

Boilerplate gunk.

...

Bah, that's a huge patch - it could use some splitting.

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--


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