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
* 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);
-
if (process_efi_entries(minimum, image_size))
return slots_fetch_random();
@@ -831,8 +828,8 @@ void choose_random_location(unsigned long input,
/*
* Low end of the randomization range should be the
- * smaller of 512M or the initial kernel image
- * location:
+ * smaller of 512M or the initial kernel image location.
+ * Should be aligned to CONFIG_PHYSICAL_ALIGN.
*/
min_addr = min(*output, 512UL << 20);
--
2.17.0
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.
> * 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.
> if (process_efi_entries(minimum, image_size))
> return slots_fetch_random();
>
> @@ -831,8 +828,8 @@ void choose_random_location(unsigned long input,
>
> /*
> * Low end of the randomization range should be the
> - * smaller of 512M or the initial kernel image
> - * location:
> + * smaller of 512M or the initial kernel image location.
> + * Should be aligned to CONFIG_PHYSICAL_ALIGN.
This is fine to mention, sure.
-Kees
> */
> min_addr = min(*output, 512UL << 20);
>
> --
> 2.17.0
>
>
>
--
Kees Cook
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
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.
>
Finally see why I am wrong here, I mixed up with the input_size & ZO
image file size. Sorry for the noise, and thanks very much for your
hint, Kees!
--
Sincerely,
Cao jin