ARM: 6051/1: VFP: preserve the HW context when calling signal handlers

From: Imre Deak <imre.deak@nokia.com>

Signal handlers can use floating point, so prevent them to corrupt
the main thread's VFP context. So far there were two signal stack
frame formats defined based on the VFP implementation, but the user
struct used for ptrace covers all posibilities, so use it for the
signal stack too.

Introduce also a new user struct for VFP exception registers. In
this too fields not relevant to the current VFP architecture are
ignored.

Support to save / restore the exception registers was added by
Will Deacon.

Signed-off-by: Imre Deak <imre.deak@nokia.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

3 files changed, 111 insertions, 17 deletions

diff --git a/arch/arm/include/asm/ucontext.h b/arch/arm/include/asm/ucontext.h
index bf65e9f4525d..47f023aa8495 100644
--- a/arch/arm/include/asm/ucontext.h
+++ b/arch/arm/include/asm/ucontext.h
@@ -59,23 +59,22 @@ struct iwmmxt_sigframe {
 #endif /* CONFIG_IWMMXT */
 
 #ifdef CONFIG_VFP
-#if __LINUX_ARM_ARCH__ < 6
-/* For ARM pre-v6, we use fstmiax and fldmiax.  This adds one extra
- * word after the registers, and a word of padding at the end for
- * alignment.  */
 #define VFP_MAGIC               0x56465001
-#define VFP_STORAGE_SIZE        152
-#else
-#define VFP_MAGIC               0x56465002
-#define VFP_STORAGE_SIZE        144
-#endif
 
 struct vfp_sigframe
 {
         unsigned long           magic;
         unsigned long           size;
-        union vfp_state         storage;
-};
+        struct user_vfp         ufp;
+        struct user_vfp_exc     ufp_exc;
+} __attribute__((__aligned__(8)));
+
+/*
+ *  8 byte for magic and size, 264 byte for ufp, 12 bytes for ufp_exc,
+ *  4 bytes padding.
+ */
+#define VFP_STORAGE_SIZE        sizeof(struct vfp_sigframe)
+
 #endif /* CONFIG_VFP */
 
 /*
@@ -91,7 +90,7 @@ struct aux_sigframe {
 #ifdef CONFIG_IWMMXT
         struct iwmmxt_sigframe  iwmmxt;
 #endif
-#if 0 && defined CONFIG_VFP /* Not yet saved.  */
+#ifdef CONFIG_VFP
         struct vfp_sigframe     vfp;
 #endif
         /* Something that isn't a valid magic number for any coprocessor.  */
diff --git a/arch/arm/include/asm/user.h b/arch/arm/include/asm/user.h
index df95e050f9dd..05ac4b06876a 100644
--- a/arch/arm/include/asm/user.h
+++ b/arch/arm/include/asm/user.h
@@ -83,11 +83,21 @@ struct user{
 
 /*
  * User specific VFP registers. If only VFPv2 is present, registers 16 to 31
- * are ignored by the ptrace system call.
+ * are ignored by the ptrace system call and the signal handler.
  */
 struct user_vfp {
         unsigned long long fpregs[32];
         unsigned long fpscr;
 };
 
+/*
+ * VFP exception registers exposed to user space during signal delivery.
+ * Fields not relavant to the current VFP architecture are ignored.
+ */
+struct user_vfp_exc {
+        unsigned long   fpexc;
+        unsigned long   fpinst;
+        unsigned long   fpinst2;
+};
+
 #endif /* _ARM_USER_H */
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index e7714f367eb8..907d5a620bca 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -18,6 +18,7 @@
 #include <asm/cacheflush.h>
 #include <asm/ucontext.h>
 #include <asm/unistd.h>
+#include <asm/vfp.h>
 
 #include "ptrace.h"
 #include "signal.h"
@@ -175,6 +176,90 @@ static int restore_iwmmxt_context(struct iwmmxt_sigframe *frame)
 
 #endif
 
+#ifdef CONFIG_VFP
+
+static int preserve_vfp_context(struct vfp_sigframe __user *frame)
+{
+        struct thread_info *thread = current_thread_info();
+        struct vfp_hard_struct *h = &thread->vfpstate.hard;
+        const unsigned long magic = VFP_MAGIC;
+        const unsigned long size = VFP_STORAGE_SIZE;
+        int err = 0;
+
+        vfp_sync_hwstate(thread);
+        __put_user_error(magic, &frame->magic, err);
+        __put_user_error(size, &frame->size, err);
+
+        /*
+         * Copy the floating point registers. There can be unused
+         * registers see asm/hwcap.h for details.
+         */
+        err |= __copy_to_user(&frame->ufp.fpregs, &h->fpregs,
+                              sizeof(h->fpregs));
+        /*
+         * Copy the status and control register.
+         */
+        __put_user_error(h->fpscr, &frame->ufp.fpscr, err);
+
+        /*
+         * Copy the exception registers.
+         */
+        __put_user_error(h->fpexc, &frame->ufp_exc.fpexc, err);
+        __put_user_error(h->fpinst, &frame->ufp_exc.fpinst, err);
+        __put_user_error(h->fpinst2, &frame->ufp_exc.fpinst2, err);
+
+        return err ? -EFAULT : 0;
+}
+
+static int restore_vfp_context(struct vfp_sigframe __user *frame)
+{
+        struct thread_info *thread = current_thread_info();
+        struct vfp_hard_struct *h = &thread->vfpstate.hard;
+        unsigned long magic;
+        unsigned long size;
+        unsigned long fpexc;
+        int err = 0;
+
+        __get_user_error(magic, &frame->magic, err);
+        __get_user_error(size, &frame->size, err);
+
+        if (err)
+                return -EFAULT;
+        if (magic != VFP_MAGIC || size != VFP_STORAGE_SIZE)
+                return -EINVAL;
+
+        /*
+         * Copy the floating point registers. There can be unused
+         * registers see asm/hwcap.h for details.
+         */
+        err |= __copy_from_user(&h->fpregs, &frame->ufp.fpregs,
+                                sizeof(h->fpregs));
+        /*
+         * Copy the status and control register.
+         */
+        __get_user_error(h->fpscr, &frame->ufp.fpscr, err);
+
+        /*
+         * Sanitise and restore the exception registers.
+         */
+        __get_user_error(fpexc, &frame->ufp_exc.fpexc, err);
+        /* Ensure the VFP is enabled. */
+        fpexc |= FPEXC_EN;
+        /* Ensure FPINST2 is invalid and the exception flag is cleared. */
+        fpexc &= ~(FPEXC_EX | FPEXC_FP2V);
+        h->fpexc = fpexc;
+
+        __get_user_error(h->fpinst, &frame->ufp_exc.fpinst, err);
+        __get_user_error(h->fpinst2, &frame->ufp_exc.fpinst2, err);
+
+        if (!err)
+                vfp_flush_hwstate(thread);
+
+        return err ? -EFAULT : 0;
+}
+
+#endif
+
 /*
  * Do a signal return; undo the signal stack.  These are aligned to 64-bit.
  */
@@ -233,8 +318,8 @@ static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
                 err |= restore_iwmmxt_context(&aux->iwmmxt);
 #endif
 #ifdef CONFIG_VFP
-//      if (err == 0)
-//              err |= vfp_restore_state(&sf->aux.vfp);
+        if (err == 0)
+                err |= restore_vfp_context(&aux->vfp);
 #endif
 
         return err;
@@ -348,8 +433,8 @@ setup_sigframe(struct sigframe __user *sf, struct pt_regs *regs, sigset_t *set)
                 err |= preserve_iwmmxt_context(&aux->iwmmxt);
 #endif
 #ifdef CONFIG_VFP
-//      if (err == 0)
-//              err |= vfp_save_state(&sf->aux.vfp);
+        if (err == 0)
+                err |= preserve_vfp_context(&aux->vfp);
 #endif
         __put_user_error(0, &aux->end_magic, err);