From mboxrd@z Thu Jan 1 00:00:00 1970 From: Borislav Petkov Subject: Re: [PATCH 08/29] x86/fpu: Remove fpu->initialized usage in __fpu__restore_sig() Date: Thu, 6 Dec 2018 21:07:22 +0100 Message-ID: <20181206200722.GF3986@zn.tnic> References: <20181128222035.2996-1-bigeasy@linutronix.de> <20181128222035.2996-9-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: <20181128222035.2996-9-bigeasy@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Wed, Nov 28, 2018 at 11:20:14PM +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(-) ... > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c > index d99a8ee9e185e..9c35598697b94 100644 > --- a/arch/x86/kernel/fpu/signal.c > +++ b/arch/x86/kernel/fpu/signal.c > @@ -207,11 +207,11 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size) > } > > static inline void > -sanitize_restored_xstate(struct task_struct *tsk, > +sanitize_restored_xstate(union fpregs_state *state, > struct user_i387_ia32_struct *ia32_env, > u64 xfeatures, int fx_only) > { > - struct xregs_state *xsave = &tsk->thread.fpu.state.xsave; > + struct xregs_state *xsave = &state->xsave; > struct xstate_header *header = &xsave->header; > > if (use_xsave()) { > @@ -238,7 +238,7 @@ sanitize_restored_xstate(struct task_struct *tsk, > */ > xsave->i387.mxcsr &= mxcsr_feature_mask; > > - convert_to_fxsr(tsk, ia32_env); > + convert_to_fxsr(&state->fxsave, ia32_env); > } > } > > @@ -284,8 +284,6 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > if (!access_ok(VERIFY_READ, buf, size)) > return -EACCES; > > - fpu__initialize(fpu); > - > if (!static_cpu_has(X86_FEATURE_FPU)) > return fpregs_soft_set(current, NULL, > 0, sizeof(struct user_i387_ia32_struct), > @@ -314,41 +312,34 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > * thread's fpu state, reconstruct fxstate from the fsave > * header. Validate and sanitize the copied state. > */ > + union fpregs_state *state; > + void *tmp; > struct user_i387_ia32_struct env; > int err = 0; Sort those in reverse xmas order pls. Otherwise looks ok. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.