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Reply-To: sedat.dilek@gmail.com
From:   Sedat Dilek <sedat.dilek@gmail.com>
Date:   Wed, 15 Jul 2020 11:10:33 +0200
Message-ID: <CA+icZUU_z-0Ehh3oGVY1tYkrjnuOXfMP7maRUvrmAMTH+6MdaQ@mail.gmail.com>
Subject: Re: [PATCH v5 6/7] x86/boot: Remove run-time relocations from head_{32,64}.S
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Fangrui Song <maskray@google.com>,
        Dmitry Golovin <dima@golovin.in>,
        Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Daniel Kiper <daniel.kiper@oracle.com>,
        Kees Cook <keescook@chromium.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>,
        "H . J . Lu" <hjl@sourceware.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Jul 15, 2020 at 11:03 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Wed, 15 Jul 2020 at 11:58, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > On Wed, Jul 15, 2020 at 2:41 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >
> > > The BFD linker generates run-time relocations for z_input_len and
> > > z_output_len, even though they are absolute symbols.
> > >
> > > This is fixed for binutils-2.35 [1]. Work around this for earlier
> > > versions by defining two variables input_len and output_len in addition
> > > to the symbols, and use them via position-independent references.
> > >
> > > This eliminates the last two run-time relocations in the head code and
> > > allows us to drop the -z noreloc-overflow flag to the linker.
> > >
> > > Move the -pie and --no-dynamic-linker LDFLAGS to LDFLAGS_vmlinux instead
> > > of KBUILD_LDFLAGS. There shouldn't be anything else getting linked, but
> > > this is the more logical location for these flags, and modversions might
> > > call the linker if an EXPORT_SYMBOL is left over accidentally in one of
> > > the decompressors.
> > >
> >
> > Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
> > Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
> >
> > Reported breakage with LLD in previous patchset version.
> >
>
> Please drop the bogus reported-bys. The patch does *not* address an
> issue you reported, so recording this in the commit log would be
> incorrect.
>
> Your review and testing is appreciated, and resulted in substantial
> improvements. So feel free to give your reviewed-by in addition to
> your tested-by. But reported-by is inappropriate here.
>

Correct, in a hurry I mixed it up as said in the next patch 7/7.
Please drop this Reported-by.

- Sedat -

>
> >
> > > [1] https://sourceware.org/bugzilla/show_bug.cgi?id=25754
> > >
> > > Reviewed-by: Kees Cook <keescook@chromium.org>
> > > Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
> > > Reviewed-by: Fangrui Song <maskray@google.com>
> > > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> > > ---
> > >  arch/x86/boot/compressed/Makefile  | 12 ++----------
> > >  arch/x86/boot/compressed/head_32.S | 17 ++++++++---------
> > >  arch/x86/boot/compressed/head_64.S |  4 ++--
> > >  arch/x86/boot/compressed/mkpiggy.c |  6 ++++++
> > >  4 files changed, 18 insertions(+), 21 deletions(-)
> > >
> > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > > index c829d874dcac..ae2c0dc98a6a 100644
> > > --- a/arch/x86/boot/compressed/Makefile
> > > +++ b/arch/x86/boot/compressed/Makefile
> > > @@ -51,16 +51,8 @@ UBSAN_SANITIZE :=n
> > >  KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
> > >  # Compressed kernel should be built as PIE since it may be loaded at any
> > >  # address by the bootloader.
> > > -ifeq ($(CONFIG_X86_32),y)
> > > -KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
> > > -else
> > > -# To build 64-bit compressed kernel as PIE, we disable relocation
> > > -# overflow check to avoid relocation overflow error with a new linker
> > > -# command-line option, -z noreloc-overflow.
> > > -KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \
> > > -       && echo "-z noreloc-overflow -pie --no-dynamic-linker")
> > > -endif
> > > -LDFLAGS_vmlinux := -T
> > > +LDFLAGS_vmlinux := $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
> > > +LDFLAGS_vmlinux += -T
> > >
> > >  hostprogs      := mkpiggy
> > >  HOST_EXTRACFLAGS += -I$(srctree)/tools/include
> > > diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
> > > index 8c1a4f5610f5..659fad53ca82 100644
> > > --- a/arch/x86/boot/compressed/head_32.S
> > > +++ b/arch/x86/boot/compressed/head_32.S
> > > @@ -178,18 +178,17 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
> > >  /*
> > >   * Do the extraction, and jump to the new kernel..
> > >   */
> > > -                               /* push arguments for extract_kernel: */
> > > -       pushl   $z_output_len   /* decompressed length, end of relocs */
> > > +       /* push arguments for extract_kernel: */
> > >
> > > -       pushl   %ebp            /* output address */
> > > -
> > > -       pushl   $z_input_len    /* input_len */
> > > +       pushl   output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */
> > > +       pushl   %ebp                    /* output address */
> > > +       pushl   input_len@GOTOFF(%ebx)  /* input_len */
> > >         leal    input_data@GOTOFF(%ebx), %eax
> > > -       pushl   %eax            /* input_data */
> > > +       pushl   %eax                    /* input_data */
> > >         leal    boot_heap@GOTOFF(%ebx), %eax
> > > -       pushl   %eax            /* heap area */
> > > -       pushl   %esi            /* real mode pointer */
> > > -       call    extract_kernel  /* returns kernel location in %eax */
> > > +       pushl   %eax                    /* heap area */
> > > +       pushl   %esi                    /* real mode pointer */
> > > +       call    extract_kernel          /* returns kernel location in %eax */
> > >         addl    $24, %esp
> > >
> > >  /*
> > > diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> > > index 11429092c224..9e46729cf162 100644
> > > --- a/arch/x86/boot/compressed/head_64.S
> > > +++ b/arch/x86/boot/compressed/head_64.S
> > > @@ -534,9 +534,9 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
> > >         movq    %rsi, %rdi              /* real mode address */
> > >         leaq    boot_heap(%rip), %rsi   /* malloc area for uncompression */
> > >         leaq    input_data(%rip), %rdx  /* input_data */
> > > -       movl    $z_input_len, %ecx      /* input_len */
> > > +       movl    input_len(%rip), %ecx   /* input_len */
> > >         movq    %rbp, %r8               /* output target address */
> > > -       movl    $z_output_len, %r9d     /* decompressed length, end of relocs */
> > > +       movl    output_len(%rip), %r9d  /* decompressed length, end of relocs */
> > >         call    extract_kernel          /* returns kernel location in %rax */
> > >         popq    %rsi
> > >
> > > diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c
> > > index 7e01248765b2..52aa56cdbacc 100644
> > > --- a/arch/x86/boot/compressed/mkpiggy.c
> > > +++ b/arch/x86/boot/compressed/mkpiggy.c
> > > @@ -60,6 +60,12 @@ int main(int argc, char *argv[])
> > >         printf(".incbin \"%s\"\n", argv[1]);
> > >         printf("input_data_end:\n");
> > >
> > > +       printf(".section \".rodata\",\"a\",@progbits\n");
> > > +       printf(".globl input_len\n");
> > > +       printf("input_len:\n\t.long %lu\n", ilen);
> > > +       printf(".globl output_len\n");
> > > +       printf("output_len:\n\t.long %lu\n", (unsigned long)olen);
> > > +
> > >         retval = 0;
> > >  bail:
> > >         if (f)
> > > --
> > > 2.26.2
> > >