From mboxrd@z Thu Jan 1 00:00:00 1970 From: Borislav Petkov Subject: Re: [PATCH 01/22] x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig() Date: Mon, 14 Jan 2019 17:24:00 +0100 Message-ID: <20190114162400.GN2773@zn.tnic> References: <20190109114744.10936-1-bigeasy@linutronix.de> <20190109114744.10936-2-bigeasy@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Andy Lutomirski , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , kvm@vger.kernel.org, "Jason A. Donenfeld" , Rik van Riel , Dave Hansen To: Sebastian Andrzej Siewior Return-path: Content-Disposition: inline In-Reply-To: <20190109114744.10936-2-bigeasy@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Wed, Jan 09, 2019 at 12:47:23PM +0100, Sebastian Andrzej Siewior wrote: > This is a preparation for the removal of the ->initialized member in the > fpu struct. > __fpu__restore_sig() is deactivating the FPU via fpu__drop() and then > setting manually ->initialized followed by fpu__restore(). The result is > that it is possible to manipulate fpu->state and the state of registers > won't be saved/restored on a context switch which would overwrite > fpu->state. > > Don't access the fpu->state while the content is read from user space > and examined / sanitized. Use a temporary kmalloc() buffer for the > preparation of the FPU registers and once the state is considered okay, > load it. Should something go wrong, return with an error and without > altering the original FPU registers. > > The removal of "fpu__initialize()" is a nop because fpu->initialized is > already set for the user task. > > Signed-off-by: Sebastian Andrzej Siewior > --- > arch/x86/include/asm/fpu/signal.h | 2 +- > arch/x86/kernel/fpu/regset.c | 5 ++-- > arch/x86/kernel/fpu/signal.c | 41 ++++++++++++------------------- > 3 files changed, 19 insertions(+), 29 deletions(-) ... > @@ -315,40 +313,33 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > * header. Validate and sanitize the copied state. > */ > struct user_i387_ia32_struct env; > + union fpregs_state *state; > int err = 0; > + void *tmp; > > - /* > - * Drop the current fpu which clears fpu->initialized. This ensures > - * that any context-switch during the copy of the new state, > - * avoids the intermediate state from getting restored/saved. > - * Thus avoiding the new restored state from getting corrupted. > - * We will be ready to restore/save the state only after > - * fpu->initialized is again set. > - */ > - fpu__drop(fpu); > + tmp = kzalloc(sizeof(*state) + fpu_kernel_xstate_size + 64, GFP_KERNEL); > + if (!tmp) > + return -ENOMEM; > + state = PTR_ALIGN(tmp, 64); > > if (using_compacted_format()) { > - err = copy_user_to_xstate(&fpu->state.xsave, buf_fx); > + err = copy_user_to_xstate(&state->xsave, buf_fx); > } else { > - err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size); > + err = __copy_from_user(&state->xsave, buf_fx, state_size); > > if (!err && state_size > offsetof(struct xregs_state, header)) > - err = validate_xstate_header(&fpu->state.xsave.header); > + err = validate_xstate_header(&state->xsave.header); > } > > if (err || __copy_from_user(&env, buf, sizeof(env))) { > - fpstate_init(&fpu->state); > - trace_x86_fpu_init_state(fpu); > err = -1; > } else { > - sanitize_restored_xstate(tsk, &env, xfeatures, fx_only); > + sanitize_restored_xstate(state, &env, > + xfeatures, fx_only); Just let that one stick out - there are other lines in this file already longer than 80. Notwithstanding, I don't see anything wrong with this patch. Acked-by: Borislav Petkov -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.