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Message-ID: <CAJcbSZFeY-1ne1cYG0zW7ETRp1MyGkz7SSMzvWckWtUS82DMqg@mail.gmail.com>
Date: Wed, 5 Apr 2017 07:36:17 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>, Heiko Carstens <heiko.carstens@...ibm.com>,
Dave Hansen <dave.hansen@...el.com>, Arnd Bergmann <arnd@...db.de>,
Thomas Gleixner <tglx@...utronix.de>, Al Viro <viro@...iv.linux.org.uk>,
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Andrew Morton <akpm@...ux-foundation.org>,
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Oleg Nesterov <oleg@...hat.com>, Stephen Smalley <sds@...ho.nsa.gov>,
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Subject: Re: [PATCH v6 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state
On Wed, Apr 5, 2017 at 7:22 AM, Catalin Marinas <catalin.marinas@....com> wrote:
> On Tue, Apr 04, 2017 at 10:47:27AM -0700, Thomas Garnier wrote:
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index 43512d4d7df2..6d598e7051c3 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -744,6 +744,10 @@ ENDPROC(cpu_switch_to)
>> ret_fast_syscall:
>> disable_irq // disable interrupts
>> str x0, [sp, #S_X0] // returned x0
>> + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change
>> + mov x1, #TASK_SIZE_64
>> + cmp x2, x1
>> + b.ne addr_limit_fail
>
> KERNEL_DS is set to the maximum address (-1UL), so it would be easier to
> check against this here and avoid a "mov". Even simpler if you'd check
> against bit 63 of the address for KERNEL_DS:
We also want to catch corruption so checking the 63 bit make sense. I
will look for this change in the next iteration.
>
> ldr x1, [tsk, TSK_TI_ADDR_LIMIT] // check addr limit change
> tbnz x1, #63, addr_limit_fail // KERNEL_DS is -1UL
>
>> ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing
>> and x2, x1, #_TIF_SYSCALL_WORK
>> cbnz x2, ret_fast_syscall_trace
>> @@ -771,6 +775,11 @@ work_pending:
>> */
>> ret_to_user:
>> disable_irq // disable interrupts
>> + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change
>> + mov x1, #TASK_SIZE_64
>> + cmp x2, x1
>> + b.ne addr_limit_fail
>
> Same here.
>
>> +
>> ldr x1, [tsk, #TSK_TI_FLAGS]
>> and x2, x1, #_TIF_WORK_MASK
>> cbnz x2, work_pending
>> @@ -779,6 +788,12 @@ finish_ret_to_user:
>> kernel_exit 0
>> ENDPROC(ret_to_user)
>>
>> +addr_limit_fail:
>> + stp x0, lr, [sp,#-16]!
>> + bl asm_verify_pre_usermode_state
>> + ldp x0, lr, [sp],#16
>> + ret lr
>
> Where is this supposed to return? What is the value of lr when branching
> to addr_limit_fail?
It is not supposed to return. Do you think I should remove stp, ldp,
ret and jut add a brk 0x100 or jmp/call a break/bug function?
>
> --
> Catalin
--
Thomas
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