Messages in this thread | | | Date | Mon, 7 Mar 2016 14:35:15 -0800 | Subject | Re: [PATCH v3 02/19] x86, boot: Move compressed kernel to end of buffer before decompressing | From | Kees Cook <> |
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On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <bhe@redhat.com> wrote: > From: Yinghai Lu <yinghai@kernel.org> > > For better understanding clarify what are VO and ZO firstly. They are > introduced in below commits by hpa. > 77d1a49 x86, boot: make symbols from the main vmlinux available > 37ba7ab x86, boot: make kernel_alignment adjustable; new bzImage fields > > VO: > - uncompressed kernel > - size: VO__end - VO__text > > ZO: > - boot/compressed/vmlinux > - head text + compressed (VO+relocs) + decompressor code > - size: ZO__end - ZO_startup_32 > > And also copy INIT_SIZE definition here for reference. From below macros > we can see INIT_SIZE is either bigger than VO_INIT_SIZE or equal to > VO_INIT_SIZE. > > #define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset) > #define VO_INIT_SIZE (VO__end - VO__text) > #if ZO_INIT_SIZE > VO_INIT_SIZE > #define INIT_SIZE ZO_INIT_SIZE > #else > #define INIT_SIZE VO_INIT_SIZE > #endif > > Current code uses extract_offset to decide the copied ZO position, it > put ZO starting from extract_offset. When INIT_SIZE is bigger than > VO_INIT_SIZE copied ZO occupies space from extract_offset to the end > of decompressing buffer, just like below. > > 0 extract_offset init_size > |-----------|---------------|------------------------|---------| > | | | | > VO__text startup_32 of ZO VO__end ZO__end > > However when INIT_SIZE is euqal to VO_INIT_SIZE there's still space left
typo: "equal"
> from end of ZO to the end of decompressing buffer, like below. > > 0 extract_offset init_size > |-----------|---------------|------------------------|---------| > | | | | > VO__text startup_32 of ZO ZO__end VO__end > > It's better to always put ZO right in the end of decompressing buffer. > Anyway, who doesn't like it to be better.
It looks to me like it's just cleaner to always have ZO__end == VO__end? Is that the motivation for moving it? What problem is solved with this change?
-Kees
> > So in this patch add BP_init_size into asm-offsets.c to make it visible > to asm modules. And find the starting position of copied ZO by init_size > and ZO run size, namely (ZO__end - startup_32) when move ZO. > > Signed-off-by: Yinghai Lu <yinghai@kernel.org> > --- > v2->v3: > Adjust the patch log. > > arch/x86/boot/compressed/head_32.S | 11 +++++++++-- > arch/x86/boot/compressed/head_64.S | 8 ++++++-- > arch/x86/boot/compressed/mkpiggy.c | 3 --- > arch/x86/boot/compressed/vmlinux.lds.S | 1 + > arch/x86/kernel/asm-offsets.c | 1 + > arch/x86/kernel/vmlinux.lds.S | 1 + > 6 files changed, 18 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S > index 8ef964d..0c140f9 100644 > --- a/arch/x86/boot/compressed/head_32.S > +++ b/arch/x86/boot/compressed/head_32.S > @@ -148,7 +148,9 @@ preferred_addr: > 1: > > /* Target address to relocate to for decompression */ > - addl $z_extract_offset, %ebx > + movl BP_init_size(%esi), %eax > + subl $_end, %eax > + addl %eax, %ebx > > /* Set up the stack */ > leal boot_stack_end(%ebx), %esp > @@ -210,8 +212,13 @@ relocated: > /* push arguments for decompress_kernel: */ > pushl $z_run_size /* size of kernel with .bss and .brk */ > pushl $z_output_len /* decompressed length, end of relocs */ > - leal z_extract_offset_negative(%ebx), %ebp > + > + movl BP_init_size(%esi), %eax > + subl $_end, %eax > + movl %ebx, %ebp > + subl %eax, %ebp > pushl %ebp /* output address */ > + > pushl $z_input_len /* input_len */ > leal input_data(%ebx), %eax > pushl %eax /* input_data */ > diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S > index b0c0d16..67dd8d3 100644 > --- a/arch/x86/boot/compressed/head_64.S > +++ b/arch/x86/boot/compressed/head_64.S > @@ -102,7 +102,9 @@ ENTRY(startup_32) > 1: > > /* Target address to relocate to for decompression */ > - addl $z_extract_offset, %ebx > + movl BP_init_size(%esi), %eax > + subl $_end, %eax > + addl %eax, %ebx > > /* > * Prepare for entering 64 bit mode > @@ -330,7 +332,9 @@ preferred_addr: > 1: > > /* Target address to relocate to for decompression */ > - leaq z_extract_offset(%rbp), %rbx > + movl BP_init_size(%rsi), %ebx > + subl $_end, %ebx > + addq %rbp, %rbx > > /* Set up the stack */ > leaq boot_stack_end(%rbx), %rsp > diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c > index d8222f2..b980046 100644 > --- a/arch/x86/boot/compressed/mkpiggy.c > +++ b/arch/x86/boot/compressed/mkpiggy.c > @@ -85,9 +85,6 @@ int main(int argc, char *argv[]) > printf("z_output_len = %lu\n", (unsigned long)olen); > printf(".globl z_extract_offset\n"); > printf("z_extract_offset = 0x%lx\n", offs); > - /* z_extract_offset_negative allows simplification of head_32.S */ > - printf(".globl z_extract_offset_negative\n"); > - printf("z_extract_offset_negative = -0x%lx\n", offs); > printf(".globl z_run_size\n"); > printf("z_run_size = %lu\n", run_size); > > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S > index 34d047c..e24e0a0 100644 > --- a/arch/x86/boot/compressed/vmlinux.lds.S > +++ b/arch/x86/boot/compressed/vmlinux.lds.S > @@ -70,5 +70,6 @@ SECTIONS > _epgtable = . ; > } > #endif > + . = ALIGN(PAGE_SIZE); /* keep ZO size page aligned */ > _end = .; > } > diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c > index 84a7524..506de14 100644 > --- a/arch/x86/kernel/asm-offsets.c > +++ b/arch/x86/kernel/asm-offsets.c > @@ -81,6 +81,7 @@ void common(void) { > OFFSET(BP_hardware_subarch, boot_params, hdr.hardware_subarch); > OFFSET(BP_version, boot_params, hdr.version); > OFFSET(BP_kernel_alignment, boot_params, hdr.kernel_alignment); > + OFFSET(BP_init_size, boot_params, hdr.init_size); > OFFSET(BP_pref_address, boot_params, hdr.pref_address); > OFFSET(BP_code32_start, boot_params, hdr.code32_start); > > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S > index 74e4bf1..217d5b1 100644 > --- a/arch/x86/kernel/vmlinux.lds.S > +++ b/arch/x86/kernel/vmlinux.lds.S > @@ -325,6 +325,7 @@ SECTIONS > __brk_limit = .; > } > > + . = ALIGN(PAGE_SIZE); /* keep VO_INIT_SIZE page aligned */ > _end = .; > > STABS_DEBUG > -- > 2.5.0 >
-- Kees Cook Chrome OS & Brillo Security
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