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Date: Wed, 5 Apr 2017 15:22:25 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Thomas Garnier <thgarnie@...gle.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>,
David Howells <dhowells@...hat.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
Andrew Morton <akpm@...ux-foundation.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Kees Cook <keescook@...omium.org>, Rik van Riel <riel@...hat.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Russell King <linux@...linux.org.uk>,
Will Deacon <will.deacon@....com>,
Mark Rutland <mark.rutland@....com>,
James Morse <james.morse@....com>, linux-s390@...r.kernel.org,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
x86@...nel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 4/4] arm64/syscalls: Specific usage of
verify_pre_usermode_state
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:
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?
--
Catalin
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