| Message ID | 20170628170411.28864-3-bsingharora@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
From: Balbir Singh > Sent: 28 June 2017 18:04 > For CONFIG_STRICT_KERNEL_RWX align __init_begin to 16M. > We use 16M since its the larger of 2M on radix and 16M > on hash for our linear mapping. The plan is to have > .text, .rodata and everything upto __init_begin marked > as RX. Note we still have executable read only data. > We could further align rodata to another 16M boundary. > I've used keeping text plus rodata as read-only-executable > as a trade-off to doing read-only-executable for text and > read-only for rodata. ... Doesn't this go against 'address space randomisation'? (Yes I realise a PIC kernel is probably non-trivial to compile and load.) David
On Thu, Jun 29, 2017 at 9:29 PM, David Laight <David.Laight@aculab.com> wrote: > From: Balbir Singh >> Sent: 28 June 2017 18:04 >> For CONFIG_STRICT_KERNEL_RWX align __init_begin to 16M. >> We use 16M since its the larger of 2M on radix and 16M >> on hash for our linear mapping. The plan is to have >> .text, .rodata and everything upto __init_begin marked >> as RX. Note we still have executable read only data. >> We could further align rodata to another 16M boundary. >> I've used keeping text plus rodata as read-only-executable >> as a trade-off to doing read-only-executable for text and >> read-only for rodata. > ... > > Doesn't this go against 'address space randomisation'? > (Yes I realise a PIC kernel is probably non-trivial to compile > and load.) I presume you mean Kernel ASLR. I am not sure why you think it goes against KASLR, it's just aligning the _stext and __init_begin, they can be anywhere in memory. I've tested with a relocatable kernel Balbir Singh.
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index ace6b65..b1a2505 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -8,6 +8,12 @@ #include <asm/cache.h> #include <asm/thread_info.h> +#ifdef CONFIG_STRICT_KERNEL_RWX +#define STRICT_ALIGN_SIZE (1 << 24) +#else +#define STRICT_ALIGN_SIZE PAGE_SIZE +#endif + ENTRY(_stext) PHDRS { @@ -123,7 +129,7 @@ SECTIONS PROVIDE32 (etext = .); /* Read-only data */ - RODATA + RO_DATA(PAGE_SIZE) EXCEPTION_TABLE(0) @@ -140,7 +146,7 @@ SECTIONS /* * Init sections discarded at runtime */ - . = ALIGN(PAGE_SIZE); + . = ALIGN(STRICT_ALIGN_SIZE); __init_begin = .; INIT_TEXT_SECTION(PAGE_SIZE) :kernel
For CONFIG_STRICT_KERNEL_RWX align __init_begin to 16M. We use 16M since its the larger of 2M on radix and 16M on hash for our linear mapping. The plan is to have .text, .rodata and everything upto __init_begin marked as RX. Note we still have executable read only data. We could further align rodata to another 16M boundary. I've used keeping text plus rodata as read-only-executable as a trade-off to doing read-only-executable for text and read-only for rodata. We don't use multi PT_LOAD in PHDRS because we are not sure if all bootloaders support them. This patch keeps PHDRS in vmlinux.lds.S as the same they are with just one PT_LOAD for all of the kernel marked as RWX (7). Signed-off-by: Balbir Singh <bsingharora@gmail.com> --- arch/powerpc/kernel/vmlinux.lds.S | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)