On Fri, Jul 31, 2020 at 4:08 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > From: Arvind Sankar <nivedita@xxxxxxxxxxxx> > > 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. > > [1] https://sourceware.org/bugzilla/show_bug.cgi?id=25754 > > Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx> > Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> > Signed-off-by: Arvind Sankar <nivedita@xxxxxxxxxxxx> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > 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 489fea16bcfb..7db0102a573d 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) $(call ld-option, --no-dynamic-linker) Oh, do these still need ld-option? bfd and lld both support these flags. (Though in their --help, they mention single hyphen and double hyphen respectively. Also, if we don't build this as PIE because the linker doesn't support the option, we probably want to fail the build? > +LDFLAGS_vmlinux += -T > > hostprogs := mkpiggy > HOST_EXTRACFLAGS += -I$(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) > -- > 2.25.1 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200731230820.1742553-7-keescook%40chromium.org. -- Thanks, ~Nick Desaulniers
