[stable:PATCH] arm64: Rework valid_user_regs (v3.16)

[Ben Hutchings]

On Mon, 2016-07-18 at 13:27 +0100, James Morse wrote:
> From: Mark Rutland <mark.rutland at arm.com>
> 
> commit dbd4d7ca563fd0a8949718d35ce197e5642d5d9d upstream.
> 
> We validate pstate using PSR_MODE32_BIT, which is part of the
> user-provided pstate (and cannot be trusted). Also, we conflate
> validation of AArch32 and AArch64 pstate values, making the code
> difficult to reason about.
> 
> Instead, validate the pstate value based on the associated task. The
> task may or may not be current (e.g. when using ptrace), so this must be
> passed explicitly by callers. To avoid circular header dependencies via
> sched.h, is_compat_task is pulled out of asm/ptrace.h.
> 
> To make the code possible to reason about, the AArch64 and AArch32
> validation is split into separate functions. Software must respect the
> RES0 policy for SPSR bits, and thus the kernel mirrors the hardware
> policy (RAZ/WI) for bits as-yet unallocated. When these acquire an
> architected meaning writes may be permitted (potentially with additional
> validation).
> 
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> [ rebased for v3.16
>   This avoids a user-triggerable Oops() if a task is switched to a mode
>   not supported by the kernel (e.g. switching a 64-bit task to AArch32).
> 
>   v3.16 does not support SETEND, support for this was added by
>   2d888f48e056 ("arm64: Emulate SETEND for AArch32 tasks") in v3.20
>   This backport forces the kernel endianness on userspace.
> 
>   Added a DBG_SPSR_SS define hidden by #ifdefs to avoid conflicts with
>   other backports.
> ]
> Signed-off-by: James Morse <james.morse at arm.com>
> Cc: <stable at vger.kernel.org> #3.16.x
[...]

Belatedly queued this up for 3.16.

Ben.

-- 
Ben Hutchings
compatible: Gracefully accepts erroneous data from any source

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