x86, xsave: save/restore the extended state context in sigframe

On cpu's supporting xsave/xrstor, fpstate pointer in the sigcontext, will
include the extended state information along with fpstate information. Presence
of extended state information is indicated by the presence
of FP_XSTATE_MAGIC1 at fpstate.sw_reserved.magic1 and FP_XSTATE_MAGIC2
at fpstate + (fpstate.sw_reserved.extended_size - FP_XSTATE_MAGIC2_SIZE).

Extended feature bit mask that is saved in the memory layout is represented
by the fpstate.sw_reserved.xstate_bv

For RT signal frames, UC_FP_XSTATE in the uc_flags also indicate the
presence of extended state information in the sigcontext's fpstate
pointer.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 162 insertions, 10 deletions

diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 608e72d7ca64..dd66d0714c18 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -6,12 +6,68 @@
 #include <linux/bootmem.h>
 #include <linux/compat.h>
 #include <asm/i387.h>
+#ifdef CONFIG_IA32_EMULATION
+#include <asm/sigcontext32.h>
+#endif
 
 /*
  * Supported feature mask by the CPU and the kernel.
  */
 unsigned int pcntxt_hmask, pcntxt_lmask;
 
+struct _fpx_sw_bytes fx_sw_reserved;
+#ifdef CONFIG_IA32_EMULATION
+struct _fpx_sw_bytes fx_sw_reserved_ia32;
+#endif
+
+/*
+ * Check for the presence of extended state information in the
+ * user fpstate pointer in the sigcontext.
+ */
+int check_for_xstate(struct i387_fxsave_struct __user *buf,
+                     void __user *fpstate,
+                     struct _fpx_sw_bytes *fx_sw_user)
+{
+        int min_xstate_size = sizeof(struct i387_fxsave_struct) +
+                              sizeof(struct xsave_hdr_struct);
+        unsigned int magic2;
+        int err;
+
+        err = __copy_from_user(fx_sw_user, &buf->sw_reserved[0],
+                               sizeof(struct _fpx_sw_bytes));
+
+        if (err)
+                return err;
+
+        /*
+         * First Magic check failed.
+         */
+        if (fx_sw_user->magic1 != FP_XSTATE_MAGIC1)
+                return -1;
+
+        /*
+         * Check for error scenarios.
+         */
+        if (fx_sw_user->xstate_size < min_xstate_size ||
+            fx_sw_user->xstate_size > xstate_size ||
+            fx_sw_user->xstate_size > fx_sw_user->extended_size)
+                return -1;
+
+        err = __get_user(magic2, (__u32 *) (((void *)fpstate) +
+                                            fx_sw_user->extended_size -
+                                            FP_XSTATE_MAGIC2_SIZE));
+        /*
+         * Check for the presence of second magic word at the end of memory
+         * layout. This detects the case where the user just copied the legacy
+         * fpstate layout with out copying the extended state information
+         * in the memory layout.
+         */
+        if (err || magic2 != FP_XSTATE_MAGIC2)
+                return -1;
+
+        return 0;
+}
+
 #ifdef CONFIG_X86_64
 /*
  * Signal frame handlers.
@@ -28,15 +84,18 @@ int save_i387_xstate(void __user *buf)
         BUILD_BUG_ON(sizeof(struct user_i387_struct) !=
                         sizeof(tsk->thread.xstate->fxsave));
 
-        if ((unsigned long)buf % 16)
+        if ((unsigned long)buf % 64)
                 printk("save_i387_xstate: bad fpstate %p\n", buf);
 
         if (!used_math())
                 return 0;
         clear_used_math(); /* trigger finit */
         if (task_thread_info(tsk)->status & TS_USEDFPU) {
-                err = save_i387_checking((struct i387_fxsave_struct __user *)
-                                         buf);
+                if (task_thread_info(tsk)->status & TS_XSAVE)
+                        err = xsave_user(buf);
+                else
+                        err = fxsave_user(buf);
+
                 if (err)
                         return err;
                 task_thread_info(tsk)->status &= ~TS_USEDFPU;
@@ -46,23 +105,77 @@ int save_i387_xstate(void __user *buf)
                                    xstate_size))
                         return -1;
         }
+
+        if (task_thread_info(tsk)->status & TS_XSAVE) {
+                struct _fpstate __user *fx = buf;
+
+                err = __copy_to_user(&fx->sw_reserved, &fx_sw_reserved,
+                                     sizeof(struct _fpx_sw_bytes));
+
+                err |= __put_user(FP_XSTATE_MAGIC2,
+                                  (__u32 __user *) (buf + sig_xstate_size
+                                                    - FP_XSTATE_MAGIC2_SIZE));
+        }
+
         return 1;
 }
 
 /*
+ * Restore the extended state if present. Otherwise, restore the FP/SSE
+ * state.
+ */
+int restore_user_xstate(void __user *buf)
+{
+        struct _fpx_sw_bytes fx_sw_user;
+        unsigned int lmask, hmask;
+        int err;
+
+        if (((unsigned long)buf % 64) ||
+             check_for_xstate(buf, buf, &fx_sw_user))
+                goto fx_only;
+
+        lmask = fx_sw_user.xstate_bv;
+        hmask = fx_sw_user.xstate_bv >> 32;
+
+        /*
+         * restore the state passed by the user.
+         */
+        err = xrestore_user(buf, lmask, hmask);
+        if (err)
+                return err;
+
+        /*
+         * init the state skipped by the user.
+         */
+        lmask = pcntxt_lmask & ~lmask;
+        hmask = pcntxt_hmask & ~hmask;
+
+        xrstor_state(init_xstate_buf, lmask, hmask);
+
+        return 0;
+
+fx_only:
+        /*
+         * couldn't find the extended state information in the
+         * memory layout. Restore just the FP/SSE and init all
+         * the other extended state.
+         */
+        xrstor_state(init_xstate_buf, pcntxt_lmask & ~XSTATE_FPSSE,
+                     pcntxt_hmask);
+        return fxrstor_checking((__force struct i387_fxsave_struct *)buf);
+}
+
+/*
  * This restores directly out of user space. Exceptions are handled.
  */
 int restore_i387_xstate(void __user *buf)
 {
         struct task_struct *tsk = current;
-        int err;
+        int err = 0;
 
         if (!buf) {
-                if (used_math()) {
-                        clear_fpu(tsk);
-                        clear_used_math();
-                }
-
+                if (used_math())
+                        goto clear;
                 return 0;
         } else
                 if (!access_ok(VERIFY_READ, buf, sig_xstate_size))
@@ -78,12 +191,17 @@ int restore_i387_xstate(void __user *buf)
                 clts();
                 task_thread_info(current)->status |= TS_USEDFPU;
         }
-        err = fxrstor_checking((__force struct i387_fxsave_struct *)buf);
+        if (task_thread_info(tsk)->status & TS_XSAVE)
+                err = restore_user_xstate(buf);
+        else
+                err = fxrstor_checking((__force struct i387_fxsave_struct *)
+                                       buf);
         if (unlikely(err)) {
                 /*
                  * Encountered an error while doing the restore from the
                  * user buffer, clear the fpu state.
                  */
+clear:
                 clear_fpu(tsk);
                 clear_used_math();
         }
@@ -92,6 +210,38 @@ int restore_i387_xstate(void __user *buf)
 #endif
 
 /*
+ * Prepare the SW reserved portion of the fxsave memory layout, indicating
+ * the presence of the extended state information in the memory layout
+ * pointed by the fpstate pointer in the sigcontext.
+ * This will be saved when ever the FP and extended state context is
+ * saved on the user stack during the signal handler delivery to the user.
+ */
+void prepare_fx_sw_frame(void)
+{
+        int size_extended = (xstate_size - sizeof(struct i387_fxsave_struct)) +
+                             FP_XSTATE_MAGIC2_SIZE;
+
+        sig_xstate_size = sizeof(struct _fpstate) + size_extended;
+
+#ifdef CONFIG_IA32_EMULATION
+        sig_xstate_ia32_size = sizeof(struct _fpstate_ia32) + size_extended;
+#endif
+
+        memset(&fx_sw_reserved, 0, sizeof(fx_sw_reserved));
+
+        fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
+        fx_sw_reserved.extended_size = sig_xstate_size;
+        fx_sw_reserved.xstate_bv = pcntxt_lmask |
+                                         (((u64) (pcntxt_hmask)) << 32);
+        fx_sw_reserved.xstate_size = xstate_size;
+#ifdef CONFIG_IA32_EMULATION
+        memcpy(&fx_sw_reserved_ia32, &fx_sw_reserved,
+               sizeof(struct _fpx_sw_bytes));
+        fx_sw_reserved_ia32.extended_size = sig_xstate_ia32_size;
+#endif
+}
+
+/*
  * Represents init state for the supported extended state.
  */
 struct xsave_struct *init_xstate_buf;
@@ -162,6 +312,8 @@ void __init xsave_cntxt_init(void)
 
         xstate_size = ebx;
 
+        prepare_fx_sw_frame();
+
         setup_xstate_init();
 
         printk(KERN_INFO "xsave/xrstor: enabled xstate_bv 0x%Lx, "