From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Tue, 18 Jun 2013 11:07:15 +0100 Subject: [PATCH v6] arm: Preserve the user r/w register TPIDRURW on context, switch and fork In-Reply-To: <51BF8A1C.5070403@dawncrow.de> References: <51BF8A1C.5070403@dawncrow.de> Message-ID: <20130618100715.GA3539@mudshark.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jun 17, 2013 at 11:13:48PM +0100, Andr? Hentschel wrote: > From: Andr? Hentschel > > Since commit 6a1c53124aa1 the user writeable TLS register was zeroed to > prevent it from being used as a covert channel between two tasks. > > There are more and more applications coming to Windows RT, > Wine could support them, but mostly they expect to have > the thread environment block (TEB) in TPIDRURW. > > This patch preserves that register per thread instead of clearing it. > Unlike the TPIDRURO, which is already switched, the TPIDRURW > can be updated from userspace so needs careful treatment in the case that we > modify TPIDRURW and call fork(). To avoid this we must always read > TPIDRURW in copy_thread. > > Signed-off-by: Andr? Hentschel > Signed-off-by: Will Deacon > Signed-off-by: Jonathan Austin > > --- > This patch is against Linux 3.10-rc6 (7d132055814ef17a6c7b69f342244c410a5e000f) > > v2: rework and fixup of v1, based on a suggested patch by Will Deacon > v3: total rework and fixup of v2 > v4: removed condition on assembler instruction, > adapted my code to kernel-style, both based on comments by Will Deacon > v5: rebased v4 on 3.10-rc2 and adding this version history > v6: moved loading the TLS registers to the macros > (fixing the "LDRD is not supported on all the CPUs we have" problem) You've changed quite a lot with this version, including the way the macro parameters are passed. Why not just replace the problematic ldrd with two ldr instructions and be done with it? I don't think the simple build error warrants an overhaul of the code we already had. Cheers, Will