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Date: Thu, 10 Mar 2011 10:39:15 +0800
From: Lin Ming <ming.m.lin@...el.com>
To: matthieu castet <castet.matthieu@...e.fr>
Cc: Peter Zijlstra <peterz@...radead.org>,
Andi Kleen <andi@...stfloor.org>,
Siarhei Liakh <sliakh.lkml@...il.com>,
Xuxian Jiang <jiang@...ncsu.edu>, Ingo Molnar <mingo@...e.hu>,
Arjan van de Ven <arjan@...radead.org>,
lkml <linux-kernel@...r.kernel.org>, tglx <tglx@...utronix.de>,
"linux-security-module@...r.kernel.org"
<linux-security-module@...r.kernel.org>
Subject: Re: -tip tree resume fail, bisect to 5bd5a45(x86: Add NX
protection for kernel data)
On Thu, 2011-03-10 at 07:16 +0800, matthieu castet wrote:
> Hi,
>
> matthieu castet a écrit :
> > matthieu castet a écrit :
> >> Lin Ming a écrit :
> >>> On Tue, 2010-11-30 at 19:27 +0800, Peter Zijlstra wrote:
> >>>> On Tue, 2010-11-30 at 13:00 +0800, Lin Ming wrote:
> >>>>> echo 0 > /sys/devices/system/cpu/cpu1/online;
> >>>>> echo 1 > /sys/devices/system/cpu/cpu1/online;
> >>>>>
> >>>>> then machine just reboots...
> >>>>>
> >> I tried to do the same thing on qemu, and the same behavior happened
> >> (ie reboot when resuming cpu1).
> >>
> >> After enabling qemu log, I found that a triple fault was happening at
> >> the beginning of secondary_startup_64
> >> when doing "addq phys_base(%rip), %rax".
> >>
> >> Why ?
> >> I suppose because we access data set to NX, but we don't have enabled
> >> yet NX in the msr. So the cpu crash due to "reserved bit check".
> >>
> >> If we enable NX before reading data, there is no more crash (patch
> >> attached).
> >>
> >> Now I am not sure this is the correct fix. I think the problem is that
> >> trampoline using kernel page table
> >> is very dangerous. The kernel can have modified them atfer booting !
> >> May be all the paging stuff should have been done in head_64.S. A
> >> first one with identity mapping, and the second one for
> >> the real kernel stuff.
> >>
> > Lin, could you try this patch on your x64 machine.
> >
> >
> I updated the patch to last tip. I tested on a 64 bits config and everything works.
I tested suspend/resume/hotplug and it works on my 64 bit notebook too.
Thanks,
Lin Ming
>
> Any comment on it ?
>
>
> Thanks
>
>
> Matthieu
>
>
> From: Matthieu CASTET <castet.matthieu@...e.fr>
> Date: Thu, 10 Mar 2011 00:10:01 +0100
> Subject: [PATCH] x86 : Add NX protection for kernel data on 64 bit
>
> This fix the cpu hotplug support, by allocating dedicated page table
> for ident mapping in trampoline.
> This is need because kernel set NX flag in level3_ident_pgt and
> level3_kernel_pgt, and made it unusable from trampoline.
>
> We also set the Low kernel Mapping to NX.
>
> Finaly we apply nx in free_init_pages only when we switch to NX mode in order
> to preserve large page mapping.
>
> mapping now look like :
> ---[ Low Kernel Mapping ]---
> 0xffff880000000000-0xffff880000200000 2M RW GLB NX pte
> 0xffff880000200000-0xffff880001000000 14M RW PSE GLB NX pmd
> 0xffff880001000000-0xffff880001200000 2M ro PSE GLB NX pmd
> 0xffff880001200000-0xffff8800012ae000 696K ro GLB NX pte
> 0xffff8800012ae000-0xffff880001400000 1352K RW GLB NX pte
> 0xffff880001400000-0xffff880001503000 1036K ro GLB NX pte
> 0xffff880001503000-0xffff880001600000 1012K RW GLB NX pte
> 0xffff880001600000-0xffff880007e00000 104M RW PSE GLB NX pmd
> 0xffff880007e00000-0xffff880007ffd000 2036K RW GLB NX pte
> 0xffff880007ffd000-0xffff880008000000 12K pte
> 0xffff880008000000-0xffff880040000000 896M pmd
> 0xffff880040000000-0xffff888000000000 511G pud
> 0xffff888000000000-0xffffc90000000000 66048G pgd
> ---[ vmalloc() Area ]---
> [...]
> ---[ High Kernel Mapping ]---
> 0xffffffff80000000-0xffffffff81000000 16M pmd
> 0xffffffff81000000-0xffffffff81400000 4M ro PSE GLB x pmd
> 0xffffffff81400000-0xffffffff81600000 2M ro PSE GLB NX pmd
> 0xffffffff81600000-0xffffffff81800000 2M RW PSE GLB NX pmd
> 0xffffffff81800000-0xffffffffa0000000 488M pmd
> ---[ Modules ]---
>
> Signed-off-by: Matthieu CASTET <castet.matthieu@...e.fr>
>
> Conflicts:
>
> arch/x86/kernel/head_64.S
> ---
> arch/x86/kernel/head_64.S | 15 +++++++++++++++
> arch/x86/kernel/trampoline_64.S | 4 ++--
> arch/x86/mm/init.c | 6 ++++--
> arch/x86/mm/init_64.c | 6 +++++-
> 4 files changed, 26 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index e11e394..e261354 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -140,6 +140,9 @@ ident_complete:
> addq %rbp, trampoline_level4_pgt + 0(%rip)
> addq %rbp, trampoline_level4_pgt + (511*8)(%rip)
>
> + addq %rbp, trampoline_level3_ident_pgt + 0(%rip)
> + addq %rbp, trampoline_level3_ident_pgt + (L3_START_KERNEL*8)(%rip)
> +
> /* Due to ENTRY(), sometimes the empty space gets filled with
> * zeros. Better take a jmp than relying on empty space being
> * filled with 0x90 (nop)
> @@ -395,6 +398,18 @@ NEXT_PAGE(level2_kernel_pgt)
> NEXT_PAGE(level2_spare_pgt)
> .fill 512, 8, 0
>
> +NEXT_PAGE(trampoline_level3_ident_pgt)
> + .quad trampoline_level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
> + .fill L3_START_KERNEL-1,8,0
> + .quad trampoline_level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
> + .fill 511-L3_START_KERNEL,8,0
> +
> +
> +NEXT_PAGE(trampoline_level2_ident_pgt)
> + /* Since I easily can, map the first 1G.
> + * Don't set NX because code runs from these pages.
> + */
> + PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD)
> #undef PMDS
> #undef NEXT_PAGE
>
> diff --git a/arch/x86/kernel/trampoline_64.S b/arch/x86/kernel/trampoline_64.S
> index 09ff517..8723e47 100644
> --- a/arch/x86/kernel/trampoline_64.S
> +++ b/arch/x86/kernel/trampoline_64.S
> @@ -164,8 +164,8 @@ trampoline_stack:
> .org 0x1000
> trampoline_stack_end:
> ENTRY(trampoline_level4_pgt)
> - .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
> + .quad trampoline_level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
> .fill 510,8,0
> - .quad level3_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE
> + .quad trampoline_level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
>
> ENTRY(trampoline_end)
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 286d289..98dd5fa 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -338,8 +338,10 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
> * we are going to free part of that, we need to make that
> * writeable and non-executable first.
> */
> - set_memory_nx(begin, (end - begin) >> PAGE_SHIFT);
> - set_memory_rw(begin, (end - begin) >> PAGE_SHIFT);
> + if (kernel_set_to_readonly) {
> + set_memory_nx(begin, (end - begin) >> PAGE_SHIFT);
> + set_memory_rw(begin, (end - begin) >> PAGE_SHIFT);
> + }
>
> printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 470cc47..e9bb29d 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -832,6 +832,7 @@ void mark_rodata_ro(void)
> unsigned long rodata_start =
> ((unsigned long)__start_rodata + PAGE_SIZE - 1) & PAGE_MASK;
> unsigned long end = (unsigned long) &__end_rodata_hpage_align;
> + unsigned long kernel_end = (((unsigned long)&__init_end + HPAGE_SIZE) & HPAGE_MASK);
> unsigned long text_end = PAGE_ALIGN((unsigned long) &__stop___ex_table);
> unsigned long rodata_end = PAGE_ALIGN((unsigned long) &__end_rodata);
> unsigned long data_start = (unsigned long) &_sdata;
> @@ -842,11 +843,14 @@ void mark_rodata_ro(void)
>
> kernel_set_to_readonly = 1;
>
> + /* make low level mapping NX */
> + set_memory_nx(PAGE_OFFSET, (PMD_PAGE_SIZE*PTRS_PER_PMD) >> PAGE_SHIFT);
> +
> /*
> * The rodata section (but not the kernel text!) should also be
> * not-executable.
> */
> - set_memory_nx(rodata_start, (end - rodata_start) >> PAGE_SHIFT);
> + set_memory_nx(rodata_start, (kernel_end - rodata_start) >> PAGE_SHIFT);
>
> rodata_test();
>
--
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