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    SubjectRe: [PATCH v5 6/7] x86/boot: Remove run-time relocations from head_{32,64}.S
    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
    > > >

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