Re: [PATCH 00/11] kexec_file: Clean up purgatory load

[Dave Young]

Hi Philipp,
On 03/09/18 at 03:25pm, Philipp Rudo wrote:
> Hi Dave,
> 
> On Fri, 9 Mar 2018 13:19:40 +0800
> Dave Young <dyoung@xxxxxxxxxx> wrote:
> 
> > Hi Philipp,
> > On 02/26/18 at 04:16pm, Philipp Rudo wrote:
> > > 
> > > Hi everybody
> > > 
> > > following the discussion with Dave and AKASHI, here are the common code
> > > patches extracted from my recent patch set (Add kexec_file_load support to
> > > s390) [1]. The patches were extracted to allow upstream integration together
> > > with AKASHI's common code patches before the arch code gets adjusted to the
> > > new base.
> > > 
> > > The reason for this series is to prepare common code for adding
> > > kexec_file_load to s390 as well as cleaning up the mis-use of the sh_offset
> > > field during purgatory load. In detail this series contains:
> > > 
> > > Patch #1&2: Minor cleanups/fixes.
> > > 
> > > Patch #3-9: Clean up the purgatory load/relocation code. Especially remove
> > > the mis-use of the purgatory_info->sechdrs->sh_offset field, currently
> > > holding a pointer into either kexec_purgatory (ro) or purgatory_buf (rw)
> > > depending on the section. With these patches the section address will be
> > > calculated verbosely and sh_offset will contain the offset of the section
> > > in the stripped purgatory binary (purgatory_buf).
> > > 
> > > Patch #10: Allows architectures to set the purgatory load address. This
> > > patch is important for s390 as the kernel and purgatory have to be loaded
> > > to fixed addresses. In current code this is impossible as the purgatory
> > > load is opaque to the architecture.
> > > 
> > > Patch #11: Moves x86 purgatories sha implementation to common lib/
> > > directory to allow reuse in other architectures.
> > > 
> > > The patches apply to v4.16-rc3. There are no changes compared to [1] (all
> > > requested changes only affected s390 code). Please note that I had to touch
> > > arch code for x86 and power a little. In theory this should not change the
> > > behavior but I don't have a way to test it. Cross-compiling with
> > > defconfig [2] works fine for both.
> > > 
> > > Thanks
> > > Philipp
> > > 
> > > [1] http://lists.infradead.org/pipermail/kexec/2018-February/019926.html
> > > [2] On x86 with the orc unwinder and stack validation turned off. objtool
> > >     SEGFAULTs on s390...
> > > 
> > > Philipp Rudo (11):
> > >   kexec_file: Silence compile warnings
> > >   kexec_file: Remove checks in kexec_purgatory_load
> > >   kexec_file: Make purgatory_info->ehdr const
> > >   kexec_file: Search symbols in read-only kexec_purgatory
> > >   kexec_file: Use read-only sections in arch_kexec_apply_relocations*
> > >   kexec_file: Split up __kexec_load_puragory
> > >   kexec_file: Simplify kexec_purgatory_setup_sechdrs 1
> > >   kexec_file: Simplify kexec_purgatory_setup_sechdrs 2
> > >   kexec_file: Remove mis-use of sh_offset field
> > >   kexec_file: Allow archs to set purgatory load address
> > >   kexec_file: Move purgatories sha256 to common code
> > > 
> > >  arch/powerpc/kernel/kexec_elf_64.c             |   9 +-
> > >  arch/x86/kernel/kexec-bzimage64.c              |   8 +-
> > >  arch/x86/kernel/machine_kexec_64.c             |  66 ++---
> > >  arch/x86/purgatory/Makefile                    |   3 +
> > >  arch/x86/purgatory/purgatory.c                 |   2 +-
> > >  include/linux/kexec.h                          |  38 +--
> > >  {arch/x86/purgatory => include/linux}/sha256.h |  10 +-
> > >  kernel/kexec_file.c                            | 375 ++++++++++++-------------
> > >  {arch/x86/purgatory => lib}/sha256.c           |   4 +-
> > >  9 files changed, 244 insertions(+), 271 deletions(-)
> > >  rename {arch/x86/purgatory => include/linux}/sha256.h (63%)
> > >  rename {arch/x86/purgatory => lib}/sha256.c (99%)
> > > 
> > > -- 
> > > 2.13.5
> > >   
> > 
> > I did a test on x86, but it failed:
> > [   15.636489] kexec: Undefined symbol: memcpy
> > [   15.636496] kexec-bzImage64: Loading purgatory failed
> > [   33.603356] kexec: Undefined symbol: memcpy
> > [   33.603362] kexec-bzImage64: Loading purgatory failed
> > 
> > I think this relates to the sha256 splitting patch.
> 
> I looked into this a little closer and i think i understood what happens. 
> 
> There is no definition of memcpy in arch/x86/boot/string.c, instead it's defined
> in arch/x86/boot/string.h as __buildin_memcpy (same for memset). Thus by
> switching to linux/string.h there is no more definition for it. Leaving us with
> 
> $ readelf -s purgatory.ro
> [...]
>  45: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND memcpy
> [...]
> 
> To solve this problem I see two possibilities (example patches are at the end of
> the mail):
> 
> 1) Have arch dependent includes in lib/sha256.c
> 2) Add makefile magic so memcpy is defined
> 
> With both solutions the resulting purgatory.ro looks good. However both
> solutions aren't perfect. For example in 2) i had too mix the linux/string.h
> header with arch/x86/boot/string.c, because lib/string.c has too many
> dependencies and does not compile in the purgatory. On the other hand having
> arch dependent includes isn't that nice either ...
> 
> What's your opinion on this?

Looks like it is a mess, maybe the 1st one is better although it is also
ugly.  Ccing Ingo see if he has some idea about this. 

> 
> Thanks
> Philipp
> 
> -----
> Example solution 1
> 
> --- a/lib/sha256.c
> +++ b/lib/sha256.c
> @@ -17,9 +17,14 @@
>  
>  #include <linux/bitops.h>
>  #include <linux/sha256.h>
> -#include <linux/string.h>
>  #include <asm/byteorder.h>
>  
> +#ifdef CONFIG_X86
> +#include "../arch/x86/boot/string.h"
> +#else
> +#include <linux/string.h>
> +#endif /* CONFIG_X86 */
> +
>  static inline u32 Ch(u32 x, u32 y, u32 z)
>  {
>  	return z ^ (x & (y ^ z));
> 
> -----
> Example solution 2
> 
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -1,7 +1,8 @@
>  # SPDX-License-Identifier: GPL-2.0
>  OBJECT_FILES_NON_STANDARD := y
>  
> -purgatory-y := purgatory.o stack.o setup-x86_$(BITS).o sha256.o entry64.o string.o
> +purgatory-y := purgatory.o stack.o setup-x86_$(BITS).o sha256.o entry64.o \
> +	string.o memcpy_$(BITS).o memset_$(BITS).o
>  
>  targets += $(purgatory-y)
>  PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
> @@ -9,6 +10,15 @@ PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
>  $(obj)/sha256.o: $(srctree)/lib/sha256.c
>  	$(call if_changed_rule,cc_o_c)
>  
> +$(obj)/string.o: $(srctree)/arch/x86/boot/string.c
> +	$(call if_changed_rule,cc_o_c)
> +
> +$(obj)/memset_$(BITS).o: $(srctree)/arch/x86/lib/memset_$(BITS).S
> +	$(call if_changed_rule,as_o_S)
> +
> +$(obj)/memcpy_$(BITS).o: $(srctree)/arch/x86/lib/memcpy_$(BITS).S
> +	$(call if_changed_rule,as_o_S)
> +
>  LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
>  targets += purgatory.ro
>  
> 

Thanks
Dave