[src-draft/trunk]: src/sys/arch/aarch64 Draft fpu_kern_enter/leave on aarch64.

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src-all/rev/27c67fb8fc44
branches:  trunk
changeset: 934705:27c67fb8fc44
user:      Taylor R Campbell <riastradh%NetBSD.org@localhost>
date:      Thu Jun 04 03:23:00 2020 +0000

description:
Draft fpu_kern_enter/leave on aarch64.

diffstat:

 sys/arch/aarch64/aarch64/cpu.c     |   2 +
 sys/arch/aarch64/aarch64/fpu.c     |  66 ++++++++++++++++++++++++++++++++++++++
 sys/arch/aarch64/include/cpu.h     |   2 +
 sys/arch/aarch64/include/machdep.h |   5 ++-
 4 files changed, 74 insertions(+), 1 deletions(-)

diffs (120 lines):

diff -r 3afa5282ac88 -r 27c67fb8fc44 sys/arch/aarch64/aarch64/cpu.c
--- a/sys/arch/aarch64/aarch64/cpu.c    Sun Jun 14 18:06:43 2020 +0000
+++ b/sys/arch/aarch64/aarch64/cpu.c    Thu Jun 04 03:23:00 2020 +0000
@@ -133,6 +133,8 @@
        ci->ci_dev = dv;
        dv->dv_private = ci;
 
+       ci->ci_kfpu_spl = -1;
+
        arm_cpu_do_topology(ci);
        cpu_identify(ci->ci_dev, ci);
 
diff -r 3afa5282ac88 -r 27c67fb8fc44 sys/arch/aarch64/aarch64/fpu.c
--- a/sys/arch/aarch64/aarch64/fpu.c    Sun Jun 14 18:06:43 2020 +0000
+++ b/sys/arch/aarch64/aarch64/fpu.c    Thu Jun 04 03:23:00 2020 +0000
@@ -38,6 +38,7 @@
 #include <sys/lwp.h>
 #include <sys/evcnt.h>
 
+#include <aarch64/locore.h>
 #include <aarch64/reg.h>
 #include <aarch64/pcb.h>
 #include <aarch64/armreg.h>
@@ -172,3 +173,68 @@
        reg_cpacr_el1_write(CPACR_FPEN_NONE);
        __asm __volatile ("isb");
 }
+
+void
+fpu_kern_enter(void)
+{
+       struct lwp *l = curlwp;
+       struct cpu_info *ci;
+       int s;
+
+       /*
+        * Block all interrupts.  We must block preemption since -- if
+        * this is a user thread -- there is nowhere to save the kernel
+        * fpu state, and if we want this to be usable in interrupts,
+        * we can't let interrupts interfere with the fpu state in use
+        * since there's nowhere for them to save it.
+        */
+       s = splhigh();
+       ci = curcpu();
+       KASSERT(ci->ci_kfpu_spl == -1);
+       ci->ci_kfpu_spl = s;
+
+       /*
+        * If we are in a softint and have a pinned lwp, the fpu state
+        * is that of the pinned lwp, so save it there.
+        */
+       if ((l->l_pflag & LP_INTR) && (l->l_switchto != NULL))
+               l = l->l_switchto;
+       if (fpu_used_p(l))
+               fpu_save(l);
+
+       /*
+        * Enable the fpu, and wait until it is enabled before
+        * executing any further instructions.
+        */
+       reg_cpacr_el1_write(CPACR_FPEN_ALL);
+       arm_isb();
+}
+
+void
+fpu_kern_leave(void)
+{
+       static const struct fpreg zero_fpreg;
+       struct cpu_info *ci = curcpu();
+       int s;
+
+       KASSERT(ci->ci_cpl == IPL_HIGH);
+       KASSERT(ci->ci_kfpu_spl != -1);
+
+       /*
+        * Zero the fpu registers; otherwise we might leak secrets
+        * through Spectre-class attacks to userland, even if there are
+        * no bugs in fpu state management.
+        */
+       load_fpregs(&zero_fpreg);
+
+       /*
+        * Disable the fpu so that the kernel can't accidentally use
+        * it again.
+        */
+       reg_cpacr_el1_write(CPACR_FPEN_NONE);
+       arm_isb();
+
+       s = ci->ci_kfpu_spl;
+       ci->ci_kfpu_spl = -1;
+       splx(s);
+}
diff -r 3afa5282ac88 -r 27c67fb8fc44 sys/arch/aarch64/include/cpu.h
--- a/sys/arch/aarch64/include/cpu.h    Sun Jun 14 18:06:43 2020 +0000
+++ b/sys/arch/aarch64/include/cpu.h    Thu Jun 04 03:23:00 2020 +0000
@@ -89,6 +89,8 @@
        volatile u_int ci_astpending;
        volatile u_int ci_intr_depth;
 
+       int ci_kfpu_spl;
+
        /* event counters */
        struct evcnt ci_vfp_use;
        struct evcnt ci_vfp_reuse;
diff -r 3afa5282ac88 -r 27c67fb8fc44 sys/arch/aarch64/include/machdep.h
--- a/sys/arch/aarch64/include/machdep.h        Sun Jun 14 18:06:43 2020 +0000
+++ b/sys/arch/aarch64/include/machdep.h        Thu Jun 04 03:23:00 2020 +0000
@@ -142,8 +142,11 @@
 /* fpu.c */
 void fpu_attach(struct cpu_info *);
 struct fpreg;
-void load_fpregs(struct fpreg *);
+void load_fpregs(const struct fpreg *);
 void save_fpregs(struct fpreg *);
+void fpu_kern_enter(void);
+void fpu_kern_leave(void);
+
 
 #ifdef TRAP_SIGDEBUG
 #define do_trapsignal(l, signo, code, addr, trap) \