[RFC PATCH v2 2/2] ARM: VFP: preserve the HW context when calling signal handlers

[Imre Deak]

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. This patch extends the user struct and leaves
its magic number the same, in the hope that user space code does
not depend on its size and can parse the original regs w/o
problems.

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

Signed-off-by: Imre Deak <imre.deak at nokia.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>

---
 arch/arm/include/asm/ucontext.h |   19 +++-----
 arch/arm/include/asm/user.h     |    3 +
 arch/arm/kernel/signal.c        |   91 +++++++++++++++++++++++++++++++++++++--
 3 files changed, 97 insertions(+), 16 deletions(-)

diff --git a/arch/arm/include/asm/ucontext.h b/arch/arm/include/asm/ucontext.h
index bf65e9f..1c3236b 100644
--- a/arch/arm/include/asm/ucontext.h
+++ b/arch/arm/include/asm/ucontext.h
@@ -59,23 +59,18 @@ 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;
+} __attribute__((__aligned__(8)));
+
+/* 8 byte for magic and size, 272 byte for ufp */
+#define VFP_STORAGE_SIZE	sizeof(struct vfp_sigframe)
+
 #endif /* CONFIG_VFP */
 
 /*
@@ -91,7 +86,7 @@ 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 df95e05..ea7e44d 100644
--- a/arch/arm/include/asm/user.h
+++ b/arch/arm/include/asm/user.h
@@ -88,6 +88,9 @@ struct user{
 struct user_vfp {
 	unsigned long long fpregs[32];
 	unsigned long fpscr;
+	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 e7714f3..6a36851 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 +176,88 @@ 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_state(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.fpexc, err);
+	__put_user_error(h->fpinst, &frame->ufp.fpinst, err);
+	__put_user_error(h->fpinst2, &frame->ufp.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;
+
+	vfp_sync_state(thread);
+	__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.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.fpinst, err);
+	__get_user_error(h->fpinst2, &frame->ufp.fpinst2, err);
+
+	return err ? -EFAULT : 0;
+}
+
+#endif
+
 /*
  * Do a signal return; undo the signal stack.  These are aligned to 64-bit.
  */
@@ -233,8 +316,8 @@ 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 +431,8 @@ 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);
 
-- 
1.6.6