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Date: Wed, 12 Jul 2017 13:12:43 -0700
From: Laura Abbott <labbott@...hat.com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>,
linux-arm-kernel@...ts.infradead.org, kernel-hardening@...ts.openwall.com
Cc: mark.rutland@....com, labbott@...oraproject.org, will.deacon@....com,
dave.martin@....com, catalin.marinas@....com,
Andy Lutomirski <luto@...nel.org>
Subject: Re: [RFC PATCH 00/10] arm64: allow virtually mapped stacks to be
enabled
On 07/12/2017 07:44 AM, Ard Biesheuvel wrote:
> This is a fairly quick'n'dirty attempt at enabling virtually mapped
> stacks for arm64, after learning from Mark yesterday that progress
> had more or less stalled on that front.
>
> Since having actual patches to poke at is infinitely better than having
> abstract discussions about how to approach it, I threw some code together
> that:
> 1. frees up sp_el0 by promoting register x18 to 'current' pointer while in
> the kernel; flames welcome :-) (#7)
> 2. preparatory work to allow 1., i.e., to free up x18 and preserve/restore it
> correctly as a platform register (#2, #3, #4, #5, #6)
> 3. dump the entire task stack if regs->sp points elsewhere (#8)
> 4. add the code that checks for a stack overflow and dumps the task context
> before panic()king (#9, #10)
>
> (#1 is an unrelated cleanup patch for copy_page())
>
> So instead of unconditionally switching between stacks, this code simply uses
> tpidrro_el0 and sp_el0 as scratch registers in the entry-from-el1 code so that
> we have a couple of general purpose registers to play with.
>
> Tested with the following hunk applied
>
> --- a/arch/arm64/crypto/aes-cipher-core.S
> +++ b/arch/arm64/crypto/aes-cipher-core.S
> @@ -102,6 +102,11 @@ CPU_BE( rev w7, w7 )
>
> .align 5
> ENTRY(__aes_arm64_encrypt)
> + stp x29, x30, [sp, #-400]!
> + mov x29, sp
> +
> + bl __aes_arm64_encrypt
> +
> do_crypt fround, crypto_ft_tab, crypto_fl_tab
> ENDPROC(__aes_arm64_encrypt)
>
> which produces the output below at boot (provided that CONFIG_CRYPTO_AES_ARM64=y
> and CONFIG_CRYPTO_MANAGER_DISABLE_TESTS is not set). Note that the call stack is
> missing: I suppose it should be possible to display something meaningful if x29
> still points to a valid location, but I haven't looked into it yet.
>
> BUG: stack guard page was hit at ffff000009bdbf90 (stack is ffff000009bdc000..ffff000009bdffff)
> Internal error: Oops: 96000047 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 0 PID: 613 Comm: cryptomgr_test Not tainted 4.12.0-rc4-00119-g1fb2159e248e-dirty #520
> Hardware name: linux,dummy-virt (DT)
> task: ffff80007c031a00 task.stack: ffff000009bdc000
> PC is at __aes_arm64_encrypt+0x0/0x440
> LR is at __aes_arm64_encrypt+0xc/0x440
> pc : [<ffff0000080c5760>] lr : [<ffff0000080c576c>] pstate: 80000145
> sp : ffff000009bdc120
> x29: ffff000009bdc120 x28: ffff80007c181c00
> x27: 0000000000000000 x26: 0000000000000100
> x25: ffff0000089a52e8 x24: ffff000009bdfd10
> x23: 0000000000000001 x22: ffff0000089a5408
> x21: 0000000000000001 x20: ffff80007c181c08
> x19: ffff80007c220000 x18: ffff80007c031a00
> x17: 00000000002f0000 x16: ffff80007c181d24
> x15: ffff0000089b2a68 x14: 00000000000003be
> x13: 0000000000000071 x12: 00000000bf5fe8a9
> x11: 0000000000000028 x10: 000000000000002c
> x9 : ffff80007c181d20 x8 : 000000000000001b
> x7 : 0000000046d4609c x6 : ffff0000080c5fd8
> x5 : 0000000000000043 x4 : 0000000046d47b87
> x3 : 000000000000000a x2 : ffff80007c220000
> x1 : ffff80007c220000 x0 : ffff80007c181c80
> Process cryptomgr_test (pid: 613, stack limit = 0xffff000009bdc000)
> Stack: (0xffff000009bdc120 to 0xffff000009be0000)
> c120: ffff000009bdc2b0 ffff0000080c576c 0000000000000000 0000000000000000
> c140: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> <snipped ...>
> ffc0: 0000000000000000 0000000000000005 0000000000000000 0000000000000000
> ffe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> Call trace:
> Exception stack(0xffff80007efd0ad0 to 0xffff80007efd0c00)
> 0ac0: ffff80007c220000 0001000000000000
> 0ae0: ffff80007efd0ca0 ffff0000080c5760 0000000000000000 0000000000000000
> 0b00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> 0b20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> 0b40: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> 0b60: 0000000000000000 0000000000000000 ffff80007c181c80 ffff80007c220000
> 0b80: ffff80007c220000 000000000000000a 0000000046d47b87 0000000000000043
> 0ba0: ffff0000080c5fd8 0000000046d4609c 000000000000001b ffff80007c181d20
> 0bc0: 000000000000002c 0000000000000028 00000000bf5fe8a9 0000000000000071
> 0be0: 00000000000003be ffff0000089b2a68 ffff80007c181d24 00000000002f0000
> [<ffff0000080c5760>] __aes_arm64_encrypt+0x0/0x440
> Code: 00000000 00000000 00000000 00000000 (a9a77bfd)
> ---[ end trace 2c6304a96ec827cb ]---
>
> Ard Biesheuvel (10):
> arm64/lib: copy_page: use consistent prefetch stride
> arm64/lib: copy_page: avoid x18 register in assembler code
> arm64: crypto: avoid register x18 in scalar AES code
> arm64: kvm: stop treating register x18 as caller save
> arm64: kernel: avoid x18 as an arbitrary temp register
> arm64: kbuild: reserve reg x18 from general allocation by the compiler
> arm64: kernel: switch to register x18 as a task struct pointer
> arm64/kernel: dump entire stack if sp points elsewhere
> arm64: mm: add C level handling for stack overflows
> arm64: kernel: add support for virtually mapped stacks
>
> arch/arm64/Kconfig | 1 +
> arch/arm64/Makefile | 2 +-
> arch/arm64/crypto/aes-cipher-core.S | 55 ++++++++---------
> arch/arm64/include/asm/asm-uaccess.h | 3 +-
> arch/arm64/include/asm/assembler.h | 8 +--
> arch/arm64/include/asm/current.h | 6 +-
> arch/arm64/include/asm/thread_info.h | 2 +
> arch/arm64/kernel/cpu-reset.S | 4 +-
> arch/arm64/kernel/entry.S | 63 ++++++++++++++++----
> arch/arm64/kernel/head.S | 6 +-
> arch/arm64/kernel/process.c | 2 +-
> arch/arm64/kernel/traps.c | 9 ++-
> arch/arm64/kvm/hyp/entry.S | 12 ++--
> arch/arm64/lib/Makefile | 3 +-
> arch/arm64/lib/copy_page.S | 47 ++++++++-------
> arch/arm64/mm/fault.c | 24 ++++++++
> 16 files changed, 154 insertions(+), 93 deletions(-)
>
This fails to compile with 64K pages
kernel/fork.c: In function ‘free_thread_stack’:
kernel/fork.c:267:41: error: ‘THREAD_SIZE_ORDER’ undeclared (first use in this function); did you mean ‘THREAD_SIZE’?
__free_pages(virt_to_page(tsk->stack), THREAD_SIZE_ORDER);
^~~~~~~~~~~~~~~~~
THREAD_SIZE
Because THREAD_SIZE_ORDER isn't defined at all for 64K pages
#ifdef CONFIG_ARM64_4K_PAGES
#define THREAD_SIZE_ORDER 2
#elif defined(CONFIG_ARM64_16K_PAGES)
#define THREAD_SIZE_ORDER 0
#endif
I think this should just be dead code on arm64 but the asymmetric
#ifdef looks fishy to me.
Thanks,
Laura
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