Author: kib
Date: Wed Jun 13 21:10:33 2018
New Revision: 335090
URL: https://svnweb.freebsd.org/changeset/base/335090
Log:
MFC r335072:
Enable eager FPU context switch by default on amd64.
Security: CVE-2018-3665
Modified:
stable/11/sys/amd64/amd64/cpu_switch.S
stable/11/sys/amd64/amd64/fpu.c
Directory Properties:
stable/11/ (props changed)
Modified: stable/11/sys/amd64/amd64/cpu_switch.S
==============================================================================
--- stable/11/sys/amd64/amd64/cpu_switch.S Wed Jun 13 21:10:23 2018
(r335089)
+++ stable/11/sys/amd64/amd64/cpu_switch.S Wed Jun 13 21:10:33 2018
(r335090)
@@ -128,10 +128,10 @@ done_store_dr:
/* have we used fp, and need a save? */
cmpq %rdi,PCPU(FPCURTHREAD)
- jne 3f
+ jne 2f
movq PCB_SAVEFPU(%r8),%r8
clts
- cmpl $0,use_xsave
+ cmpl $0,use_xsave(%rip)
jne 1f
fxsave (%r8)
jmp 2f
@@ -143,12 +143,7 @@ ctx_switch_xsave:
/* This is patched to xsaveopt if supported, see fpuinit_bsp1() */
xsave (%r8)
movq %rcx,%rdx
-2: smsw %ax
- orb $CR0_TS,%al
- lmsw %ax
- xorl %eax,%eax
- movq %rax,PCPU(FPCURTHREAD)
-3:
+2:
/* Save is done. Now fire up new thread. Leave old vmspace. */
movq %rsi,%r12
movq %rdi,%r13
@@ -235,6 +230,8 @@ done_load_dr:
movq PCB_RBX(%r8),%rbx
movq PCB_RIP(%r8),%rax
movq %rax,(%rsp)
+ movq PCPU(CURTHREAD),%rdi
+ call fpu_activate_sw
ret
/*
Modified: stable/11/sys/amd64/amd64/fpu.c
==============================================================================
--- stable/11/sys/amd64/amd64/fpu.c Wed Jun 13 21:10:23 2018
(r335089)
+++ stable/11/sys/amd64/amd64/fpu.c Wed Jun 13 21:10:33 2018
(r335090)
@@ -139,6 +139,11 @@ static void fpu_clean_state(void);
SYSCTL_INT(_hw, HW_FLOATINGPT, floatingpoint, CTLFLAG_RD,
SYSCTL_NULL_INT_PTR, 1, "Floating point instructions executed in
hardware");
+int lazy_fpu_switch = 0;
+SYSCTL_INT(_hw, OID_AUTO, lazy_fpu_switch, CTLFLAG_RWTUN | CTLFLAG_NOFETCH,
+ &lazy_fpu_switch, 0,
+ "Lazily load FPU context after context switch");
+
int use_xsave; /* non-static for cpu_switch.S */
uint64_t xsave_mask; /* the same */
static uma_zone_t fpu_save_area_zone;
@@ -204,6 +209,7 @@ fpuinit_bsp1(void)
u_int cp[4];
uint64_t xsave_mask_user;
+ TUNABLE_INT_FETCH("hw.lazy_fpu_switch", &lazy_fpu_switch);
if ((cpu_feature2 & CPUID2_XSAVE) != 0) {
use_xsave = 1;
TUNABLE_INT_FETCH("hw.use_xsave", &use_xsave);
@@ -612,6 +618,45 @@ fputrap_sse(void)
return (fpetable[(mxcsr & (~mxcsr >> 7)) & 0x3f]);
}
+static void
+restore_fpu_curthread(struct thread *td)
+{
+ struct pcb *pcb;
+
+ /*
+ * Record new context early in case frstor causes a trap.
+ */
+ PCPU_SET(fpcurthread, td);
+
+ stop_emulating();
+ fpu_clean_state();
+ pcb = td->td_pcb;
+
+ if ((pcb->pcb_flags & PCB_FPUINITDONE) == 0) {
+ /*
+ * This is the first time this thread has used the FPU or
+ * the PCB doesn't contain a clean FPU state. Explicitly
+ * load an initial state.
+ *
+ * We prefer to restore the state from the actual save
+ * area in PCB instead of directly loading from
+ * fpu_initialstate, to ignite the XSAVEOPT
+ * tracking engine.
+ */
+ bcopy(fpu_initialstate, pcb->pcb_save,
+ cpu_max_ext_state_size);
+ fpurestore(pcb->pcb_save);
+ if (pcb->pcb_initial_fpucw != __INITIAL_FPUCW__)
+ fldcw(pcb->pcb_initial_fpucw);
+ if (PCB_USER_FPU(pcb))
+ set_pcb_flags(pcb, PCB_FPUINITDONE |
+ PCB_USERFPUINITDONE);
+ else
+ set_pcb_flags(pcb, PCB_FPUINITDONE);
+ } else
+ fpurestore(pcb->pcb_save);
+}
+
/*
* Device Not Available (DNA, #NM) exception handler.
*
@@ -622,7 +667,9 @@ fputrap_sse(void)
void
fpudna(void)
{
+ struct thread *td;
+ td = curthread;
/*
* This handler is entered with interrupts enabled, so context
* switches may occur before critical_enter() is executed. If
@@ -636,7 +683,7 @@ fpudna(void)
KASSERT((curpcb->pcb_flags & PCB_FPUNOSAVE) == 0,
("fpudna while in fpu_kern_enter(FPU_KERN_NOCTX)"));
- if (PCPU_GET(fpcurthread) == curthread) {
+ if (PCPU_GET(fpcurthread) == td) {
printf("fpudna: fpcurthread == curthread\n");
stop_emulating();
critical_exit();
@@ -645,40 +692,24 @@ fpudna(void)
if (PCPU_GET(fpcurthread) != NULL) {
panic("fpudna: fpcurthread = %p (%d), curthread = %p (%d)\n",
PCPU_GET(fpcurthread), PCPU_GET(fpcurthread)->td_tid,
- curthread, curthread->td_tid);
+ td, td->td_tid);
}
- stop_emulating();
- /*
- * Record new context early in case frstor causes a trap.
- */
- PCPU_SET(fpcurthread, curthread);
+ restore_fpu_curthread(td);
+ critical_exit();
+}
- fpu_clean_state();
+void fpu_activate_sw(struct thread *td); /* Called from the context switch */
+void
+fpu_activate_sw(struct thread *td)
+{
- if ((curpcb->pcb_flags & PCB_FPUINITDONE) == 0) {
- /*
- * This is the first time this thread has used the FPU or
- * the PCB doesn't contain a clean FPU state. Explicitly
- * load an initial state.
- *
- * We prefer to restore the state from the actual save
- * area in PCB instead of directly loading from
- * fpu_initialstate, to ignite the XSAVEOPT
- * tracking engine.
- */
- bcopy(fpu_initialstate, curpcb->pcb_save,
- cpu_max_ext_state_size);
- fpurestore(curpcb->pcb_save);
- if (curpcb->pcb_initial_fpucw != __INITIAL_FPUCW__)
- fldcw(curpcb->pcb_initial_fpucw);
- if (PCB_USER_FPU(curpcb))
- set_pcb_flags(curpcb,
- PCB_FPUINITDONE | PCB_USERFPUINITDONE);
- else
- set_pcb_flags(curpcb, PCB_FPUINITDONE);
- } else
- fpurestore(curpcb->pcb_save);
- critical_exit();
+ if (lazy_fpu_switch || (td->td_pflags & TDP_KTHREAD) != 0 ||
+ !PCB_USER_FPU(td->td_pcb)) {
+ PCPU_SET(fpcurthread, NULL);
+ start_emulating();
+ } else if (PCPU_GET(fpcurthread) != td) {
+ restore_fpu_curthread(td);
+ }
}
void
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