From: Will Deacon <will.deacon@arm•com>
To: Jiri Slaby <jslaby@suse•cz>
Cc: tglx@linutronix•de, mingo@redhat•com, dvhart@infradead•org,
peterz@infradead•org, linux-kernel@vger•kernel.org,
Richard Henderson <rth@twiddle•net>,
Ivan Kokshaysky <ink@jurassic•park.msu.ru>,
Matt Turner <mattst88@gmail•com>,
Vineet Gupta <vgupta@synopsys•com>,
Catalin Marinas <catalin.marinas@arm•com>,
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Fenghua Yu <fenghua.yu@intel•com>,
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Stafford Horne <shorne@gmail•com>,
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Subject: Re: [PATCH v2 1/1] futex: remove duplicated code and fix UB
Date: Thu, 24 Aug 2017 10:47:56 +0100 [thread overview]
Message-ID: <20170824094756.GA6346@arm.com> (raw)
In-Reply-To: <20170824073105.3901-1-jslaby@suse.cz>
Hi Jiri,
On Thu, Aug 24, 2017 at 09:31:05AM +0200, Jiri Slaby wrote:
> There is code duplicated over all architecture's headers for
> futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
> and comparison of the result.
>
> Remove this duplication and leave up to the arches only the needed
> assembly which is now in arch_futex_atomic_op_inuser.
>
> This effectively distributes the Will Deacon's arm64 fix for undefined
> behaviour reported by UBSAN to all architectures. The fix was done in
> commit 5f16a046f8e1 (arm64: futex: Fix undefined behaviour with
> FUTEX_OP_OPARG_SHIFT usage). Look there for an example dump.
>
> And as suggested by Thomas, check for negative oparg too, because it was
> also reported to cause undefined behaviour report.
>
> Note that s390 removed access_ok check in d12a29703 ("s390/uaccess:
> remove pointless access_ok() checks") as access_ok there returns true.
> We introduce it back to the helper for the sake of simplicity (it gets
> optimized away anyway).
For arm64 and the core code:
Reviewed-by: Will Deacon <will.deacon@arm•com>
Although one minor thing on the core part:
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 0939255fc750..3d38eaf05492 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1551,6 +1551,45 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
> return ret;
> }
>
> +static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
> +{
> + unsigned int op = (encoded_op & 0x70000000) >> 28;
> + unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
> + int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 12);
> + int cmparg = sign_extend32(encoded_op & 0x00000fff, 12);
> + int oldval, ret;
> +
> + if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
> + if (oparg < 0 || oparg > 31)
> + return -EINVAL;
> + oparg = 1 << oparg;
> + }
> +
> + if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
> + return -EFAULT;
> +
> + ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
> + if (ret)
> + return ret;
We could move the pagefault_{disable,enable} calls here, and then remove
them from the futex_atomic_op_inuser callsites elsewhere in futex.c
Will
next prev parent reply other threads:[~2017-08-24 9:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-24 7:31 [PATCH v2 1/1] futex: remove duplicated code and fix UB Jiri Slaby
2017-08-24 9:47 ` Will Deacon [this message]
2017-08-25 20:43 ` Thomas Gleixner
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