x86, xsave: dynamically allocate sigframes fpstate instead of static allocation

dynamically allocate fpstate on the stack, instead of static allocation
in the current sigframe layout on the user stack. This will allow the
fpstate structure to grow in the future, which includes extended state
information supporting xsave/xrstor.

signal handlers will be able to access the fpstate pointer from the
sigcontext structure asusual, with no change. For the non RT sigframe's
(which are supported only for 32bit apps), current static fpstate layout
in the sigframe will be unused(so that we don't change the extramask[]
offset in the sigframe and thus prevent breaking app's which modify
extramask[]).

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>

7 files changed, 50 insertions, 16 deletions

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 20af4c79579a..a05bf0fb7415 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -179,9 +179,10 @@ struct sigframe
         u32 pretcode;
         int sig;
         struct sigcontext_ia32 sc;
-        struct _fpstate_ia32 fpstate;
+        struct _fpstate_ia32 fpstate_unused; /* look at kernel/sigframe.h */
         unsigned int extramask[_COMPAT_NSIG_WORDS-1];
         char retcode[8];
+        /* fp state follows here */
 };
 
 struct rt_sigframe
@@ -192,8 +193,8 @@ struct rt_sigframe
         u32 puc;
         compat_siginfo_t info;
         struct ucontext_ia32 uc;
-        struct _fpstate_ia32 fpstate;
         char retcode[8];
+        /* fp state follows here */
 };
 
 #define COPY(x)         {               \
@@ -402,7 +403,8 @@ static int ia32_setup_sigcontext(struct sigcontext_ia32 __user *sc,
  * Determine which stack to use..
  */
 static void __user *get_sigframe(struct k_sigaction *ka, struct pt_regs *regs,
-                                 size_t frame_size)
+                                 size_t frame_size,
+                                 struct _fpstate_ia32 **fpstate)
 {
         unsigned long sp;
 
@@ -421,6 +423,11 @@ static void __user *get_sigframe(struct k_sigaction *ka, struct pt_regs *regs,
                  ka->sa.sa_restorer)
                 sp = (unsigned long) ka->sa.sa_restorer;
 
+        if (used_math()) {
+                sp = sp - sig_xstate_ia32_size;
+                *fpstate = (struct _fpstate_ia32 *) sp;
+        }
+
         sp -= frame_size;
         /* Align the stack pointer according to the i386 ABI,
          * i.e. so that on function entry ((sp + 4) & 15) == 0. */
@@ -434,6 +441,7 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka,
         struct sigframe __user *frame;
         void __user *restorer;
         int err = 0;
+        struct _fpstate_ia32 __user *fpstate = NULL;
 
         /* copy_to_user optimizes that into a single 8 byte store */
         static const struct {
@@ -448,7 +456,7 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka,
                 0,
         };
 
-        frame = get_sigframe(ka, regs, sizeof(*frame));
+        frame = get_sigframe(ka, regs, sizeof(*frame), &fpstate);
 
         if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
                 goto give_sigsegv;
@@ -457,8 +465,7 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka,
         if (err)
                 goto give_sigsegv;
 
-        err |= ia32_setup_sigcontext(&frame->sc, &frame->fpstate, regs,
-                                        set->sig[0]);
+        err |= ia32_setup_sigcontext(&frame->sc, fpstate, regs, set->sig[0]);
         if (err)
                 goto give_sigsegv;
 
@@ -522,6 +529,7 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
         struct rt_sigframe __user *frame;
         void __user *restorer;
         int err = 0;
+        struct _fpstate_ia32 __user *fpstate = NULL;
 
         /* __copy_to_user optimizes that into a single 8 byte store */
         static const struct {
@@ -537,7 +545,7 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 0,
         };
 
-        frame = get_sigframe(ka, regs, sizeof(*frame));
+        frame = get_sigframe(ka, regs, sizeof(*frame), &fpstate);
 
         if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
                 goto give_sigsegv;
@@ -556,7 +564,7 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
         err |= __put_user(sas_ss_flags(regs->sp),
                           &frame->uc.uc_stack.ss_flags);
         err |= __put_user(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
-        err |= ia32_setup_sigcontext(&frame->uc.uc_mcontext, &frame->fpstate,
+        err |= ia32_setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
                                      regs, set->sig[0]);
         err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
         if (err)
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index b778e17e4b01..51fb288a2c97 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -24,6 +24,7 @@
 # define save_i387_ia32         save_i387
 # define restore_i387_ia32      restore_i387
 # define _fpstate_ia32          _fpstate
+# define sig_xstate_ia32_size   sig_xstate_size
 # define user_i387_ia32_struct  user_i387_struct
 # define user32_fxsr_struct     user_fxsr_struct
 #endif
@@ -36,6 +37,7 @@
 
 static unsigned int             mxcsr_feature_mask __read_mostly = 0xffffffffu;
 unsigned int xstate_size;
+unsigned int sig_xstate_ia32_size = sizeof(struct _fpstate_ia32);
 static struct i387_fxsave_struct fx_scratch __cpuinitdata;
 
 void __cpuinit mxcsr_feature_mask_init(void)
diff --git a/arch/x86/kernel/sigframe.h b/arch/x86/kernel/sigframe.h
index 72bbb519d2dc..6dd7e2b70a4b 100644
--- a/arch/x86/kernel/sigframe.h
+++ b/arch/x86/kernel/sigframe.h
@@ -3,9 +3,18 @@ struct sigframe {
         char __user *pretcode;
         int sig;
         struct sigcontext sc;
-        struct _fpstate fpstate;
+        /*
+         * fpstate is unused. fpstate is moved/allocated after
+         * retcode[] below. This movement allows to have the FP state and the
+         * future state extensions (xsave) stay together.
+         * And at the same time retaining the unused fpstate, prevents changing
+         * the offset of extramask[] in the sigframe and thus prevent any
+         * legacy application accessing/modifying it.
+         */
+        struct _fpstate fpstate_unused;
         unsigned long extramask[_NSIG_WORDS-1];
         char retcode[8];
+        /* fp state follows here */
 };
 
 struct rt_sigframe {
@@ -15,13 +24,14 @@ struct rt_sigframe {
         void __user *puc;
         struct siginfo info;
         struct ucontext uc;
-        struct _fpstate fpstate;
         char retcode[8];
+        /* fp state follows here */
 };