Messages in this thread Patch in this message | | | Date | Sun, 10 May 2020 10:49:17 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v3 10/10] x86/fpu/xstate: Restore supervisor states for signal return |
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On Sat, Mar 28, 2020 at 09:43:07AM -0700, Yu-cheng Yu wrote: > v3: > - Change copy_xregs_to_kernel() to copy_supervisor_to_kernel(), which is > introduced in a previous patch. > - Update commit log. > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com> > --- > arch/x86/kernel/fpu/signal.c | 27 ++++++++++++++++++++++----- > 1 file changed, 22 insertions(+), 5 deletions(-)
Took Sebastian and me a while to grok the whole situation so pls add the comments below to that patch when sending it in your next revision.
Thx.
--- diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index 4dad5afc938d..06e88d6ebb07 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -347,7 +347,19 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) ret = copy_user_to_fpregs_zeroing(buf_fx, user_xfeatures, fx_only); pagefault_enable(); if (!ret) { - /* Restore supervisor states */ + + /* + * Restore supervisor states: previous context switch + * etc has done XSAVES and saved the supervisor states + * in the kernel buffer from which they can be restored + * now. + * + * We cannot do a single XRSTORS here - which would + * be nice - because the rest of the FPU registers are + * being restored from a user buffer directly. The + * single XRSTORS happens below, when the user buffer + * has been copied to the kernel one. + */ if (test_thread_flag(TIF_NEED_FPU_LOAD) && xfeatures_mask_supervisor()) copy_kernel_to_xregs(&fpu->state.xsave, @@ -369,15 +381,19 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) } /* - * Supervisor states are not modified by user space input. Save - * current supervisor states first. * By setting TIF_NEED_FPU_LOAD it is ensured that our xstate is * not modified on context switch and that the xstate is considered * to be loaded again on return to userland (overriding last_cpu avoids * the optimisation). */ fpregs_lock(); + if (!test_thread_flag(TIF_NEED_FPU_LOAD)) { + + /* + * Supervisor states are not modified by user space input. Save + * current supervisor states first and invalidate the FPU regs. + */ if (xfeatures_mask_supervisor()) copy_supervisor_to_kernel(&fpu->state.xsave); set_thread_flag(TIF_NEED_FPU_LOAD); @@ -405,6 +421,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) fpregs_lock(); if (unlikely(init_bv)) copy_kernel_to_xregs(&init_fpstate.xsave, init_bv); + /* * Restore previously saved supervisor xstates along with * copied-in user xstates.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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