| Date | Mon, 21 Jun 2021 14:05:16 +0200 | From | Borislav Petkov <> | Subject | Re: [patch V3 16/66] x86/fpu: Clean up fpregs_set() |
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On Fri, Jun 18, 2021 at 04:18:39PM +0200, Thomas Gleixner wrote: > From: Andy Lutomirski <luto@kernel.org> > > fpregs_set() has unnecessary complexity to support short or nonzero-offset > writes and to handle the case in which a copy from userspace overwrites > some of the target buffer and then fails. Support for partial writes is > useless -- just require that the write have offset 0 and the correct size, > and copy into a temporary kernel buffer to avoid clobbering the state if > the user access fails. > > Signed-off-by: Andy Lutomirski <luto@kernel.org> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > --- > V2: New patch. Picked up from Andy > --- > arch/x86/kernel/fpu/regset.c | 29 +++++++++++++++-------------- > 1 file changed, 15 insertions(+), 14 deletions(-) > --- > --- a/arch/x86/kernel/fpu/regset.c > +++ b/arch/x86/kernel/fpu/regset.c > @@ -305,31 +305,32 @@ int fpregs_set(struct task_struct *targe > struct user_i387_ia32_struct env; > int ret; > > - fpu__prepare_write(fpu); > - fpstate_sanitize_xstate(fpu); > + /* No funny business with partial or oversized writes is permitted. */ > + if (pos != 0 || count != sizeof(struct user_i387_ia32_struct)) > + return -EINVAL; > > - if (!boot_cpu_has(X86_FEATURE_FPU)) > + if (!cpu_feature_enabled(X86_FEATURE_FPU)) > return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf); > > - if (!boot_cpu_has(X86_FEATURE_FXSR)) > - return user_regset_copyin(&pos, &count, &kbuf, &ubuf, > - &fpu->state.fsave, 0, > - -1); > + ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &env, 0, -1); > + if (ret) > + return ret; > > - if (pos > 0 || count < sizeof(env)) > - convert_from_fxsr(&env, target); > + fpu__prepare_write(fpu); > > - ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &env, 0, -1); > - if (!ret) > + if (cpu_feature_enabled(X86_FEATURE_FXSR)) > convert_to_fxsr(&target->thread.fpu.state.fxsave, &env); > + else > + memcpy(&target->thread.fpu.state.fsave, &env, sizeof(env));
You have above in the prologue:
struct fpu *fpu = &target->thread.fpu;
so here you can just as well do:
if (cpu_feature_enabled(X86_FEATURE_FXSR)) convert_to_fxsr(&fpu->state.fxsave, &env); else memcpy(&fpu->state.fsave, &env, sizeof(env));
asm is identical.
With that:
Reviewed-by: Borislav Petkov <bp@suse.de>
-- Regards/Gruss, Boris.
SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg
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