On 2/1/19 4:20 PM, Kees Cook wrote: > On Fri, Feb 1, 2019 at 6:51 PM Cao jin <[email protected]> wrote: >> >> comments fix: input_size is ZO image size which just don't count .bss >> in, but has .text, .data, etc; >> drop unecessary alignment: minimum is either 512M or output, both are >> CONFIG_PHYSICAL_ALIGN aligned(output is aligned in head_32/64.S). But >> mention it in earlier comments. >> >> Signed-off-by: Cao jin <[email protected]> >> --- >> arch/x86/boot/compressed/kaslr.c | 9 +++------ >> 1 file changed, 3 insertions(+), 6 deletions(-) >> >> diff --git a/arch/x86/boot/compressed/kaslr.c >> b/arch/x86/boot/compressed/kaslr.c >> index 9ed9709d9947..a947c5aba34e 100644 >> --- a/arch/x86/boot/compressed/kaslr.c >> +++ b/arch/x86/boot/compressed/kaslr.c >> @@ -360,7 +360,7 @@ static void handle_mem_options(void) >> * (i.e. it does not include its run size). This range must be avoided >> * because it contains the data used for decompression. >> * >> - * [input+input_size, output+init_size) is [_text, _end) for ZO. This >> + * [input+input_size, output+init_size) is [_bss, _end) for ZO. This > > This isn't right. The comment was correct before. See > arch/x86/boot/compressed/vmlinux.lds.S for the layout of the ZO image: > after the compressed image is _text, _rodata, _got, _data, _bss, > _pgtable, and _end. "[_text, _end)" correctly identifies the span > used. >
I am confused, doesn't input_size = ZO image size = .head.text + .rodata..compressed + .rodata + .got + .data + .pgtable ? As I know, .bss don't occupy any space in file, and ZO's full run size is against the end of buffer, so I think the tiny gap here is just .bss, which is also the stack and heap. Do I get it wrong? >> * range includes ZO's heap and stack, and must be avoided since it >> * performs the decompression. >> * >> @@ -763,9 +763,6 @@ static unsigned long find_random_phys_addr(unsigned long >> minimum, >> return 0; >> } >> >> - /* Make sure minimum is aligned. */ >> - minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN); >> - > > I would prefer to keep this runtime calculation since it enforces the > requirement instead of making leaving it in a comment. When this goes > wrong, you get an unbootable kernel, which is very frustrating to > debug. > I find that I maybe wrong here. It is said that CONFIG_PHYSICAL_ALIGN must be a multiple of 0x200000 on 64-bit, so it could be 2M, 4M, 6M, 8M, 12M, 14M, 16M, while 512M can't be divided by 6, 10, 12, 14 without remainder. -- Sincerely, Cao jin
