um: Save FPU registers between task switches

Some time ago Jeff prepared 42daba316557 ("uml: stop saving process FP
state") for UML to stop saving the process FP state between task
switches.  The assumption was that since with SKAS0 every guest process
runs inside a host process context the host OS will take care of keeping
the proper FP state.

Unfortunately this is not true for multi-threaded applications, where
all guest threads share a single host process context yet all may use
the FPU on their own.  Although I haven't verified it I suspect things
to be even worse in SKAS3 mode where all guest processes run inside a
single host process.

The patch reintroduces the saving and restoring of the FP context
between task switches.

[richard@nod.at: Ingo posted this patch in 2009, sadly it was never applied
and got lost. Now in 2011 the problem was reported by Gunnar.]

Signed-off-by: Ingo van Lil <inguin@gmx.de>
Signed-off-by: Richard Weinberger <richard@nod.at>
Reported-by: <gunnarlindroth@hotmail.com>
Tested-by: <gunnarlindroth@hotmail.com>
Cc: Stanislav Meduna <stano@meduna.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

7 files changed, 31 insertions, 5 deletions

diff --git a/arch/um/include/shared/registers.h b/arch/um/include/shared/registers.h
index b0b4589e0ebc..f1e0aa56c52a 100644
--- a/arch/um/include/shared/registers.h
+++ b/arch/um/include/shared/registers.h
@@ -16,7 +16,7 @@ extern int restore_fpx_registers(int pid, unsigned long *fp_regs);
 extern int save_registers(int pid, struct uml_pt_regs *regs);
 extern int restore_registers(int pid, struct uml_pt_regs *regs);
 extern int init_registers(int pid);
-extern void get_safe_registers(unsigned long *regs);
+extern void get_safe_registers(unsigned long *regs, unsigned long *fp_regs);
 extern unsigned long get_thread_reg(int reg, jmp_buf *buf);
 extern int get_fp_registers(int pid, unsigned long *regs);
 extern int put_fp_registers(int pid, unsigned long *regs);
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index fab4371184f6..21c1ae7c3d75 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -202,7 +202,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
                 arch_copy_thread(&current->thread.arch, &p->thread.arch);
         }
         else {
-                get_safe_registers(p->thread.regs.regs.gp);
+                get_safe_registers(p->thread.regs.regs.gp, p->thread.regs.regs.fp);
                 p->thread.request.u.thread = current->thread.request.u.thread;
                 handler = new_thread_handler;
         }
diff --git a/arch/um/os-Linux/registers.c b/arch/um/os-Linux/registers.c
index 830fe6a1518a..b866b9e3bef9 100644
--- a/arch/um/os-Linux/registers.c
+++ b/arch/um/os-Linux/registers.c
@@ -8,6 +8,8 @@
 #include <string.h>
 #include <sys/ptrace.h>
 #include "sysdep/ptrace.h"
+#include "sysdep/ptrace_user.h"
+#include "registers.h"
 
 int save_registers(int pid, struct uml_pt_regs *regs)
 {
@@ -32,6 +34,7 @@ int restore_registers(int pid, struct uml_pt_regs *regs)
 /* This is set once at boot time and not changed thereafter */
 
 static unsigned long exec_regs[MAX_REG_NR];
+static unsigned long exec_fp_regs[FP_SIZE];
 
 int init_registers(int pid)
 {
@@ -42,10 +45,14 @@ int init_registers(int pid)
                 return -errno;
 
         arch_init_registers(pid);
+        get_fp_registers(pid, exec_fp_regs);
         return 0;
 }
 
-void get_safe_registers(unsigned long *regs)
+void get_safe_registers(unsigned long *regs, unsigned long *fp_regs)
 {
         memcpy(regs, exec_regs, sizeof(exec_regs));
+
+        if (fp_regs)
+                memcpy(fp_regs, exec_fp_regs, sizeof(exec_fp_regs));
 }
diff --git a/arch/um/os-Linux/skas/mem.c b/arch/um/os-Linux/skas/mem.c
index d261f170d120..e771398be5f3 100644
--- a/arch/um/os-Linux/skas/mem.c
+++ b/arch/um/os-Linux/skas/mem.c
@@ -39,7 +39,7 @@ static unsigned long syscall_regs[MAX_REG_NR];
 
 static int __init init_syscall_regs(void)
 {
-        get_safe_registers(syscall_regs);
+        get_safe_registers(syscall_regs, NULL);
         syscall_regs[REGS_IP_INDEX] = STUB_CODE +
                 ((unsigned long) &batch_syscall_stub -
                  (unsigned long) &__syscall_stub_start);
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index d6e0a2234b86..dee0e8cf8ad0 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -373,6 +373,9 @@ void userspace(struct uml_pt_regs *regs)
                 if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))
                         fatal_sigsegv();
 
+                if (put_fp_registers(pid, regs->fp))
+                        fatal_sigsegv();
+
                 /* Now we set local_using_sysemu to be used for one loop */
                 local_using_sysemu = get_using_sysemu();
 
@@ -399,6 +402,12 @@ void userspace(struct uml_pt_regs *regs)
                         fatal_sigsegv();
                 }
 
+                if (get_fp_registers(pid, regs->fp)) {
+                        printk(UM_KERN_ERR "userspace -  get_fp_registers failed, "
+                               "errno = %d\n", errno);
+                        fatal_sigsegv();
+                }
+
                 UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
 
                 if (WIFSTOPPED(status)) {
@@ -457,10 +466,11 @@ void userspace(struct uml_pt_regs *regs)
 }
 
 static unsigned long thread_regs[MAX_REG_NR];
+static unsigned long thread_fp_regs[FP_SIZE];
 
 static int __init init_thread_regs(void)
 {
-        get_safe_registers(thread_regs);
+        get_safe_registers(thread_regs, thread_fp_regs);
         /* Set parent's instruction pointer to start of clone-stub */
         thread_regs[REGS_IP_INDEX] = STUB_CODE +
                                 (unsigned long) stub_clone_handler -
@@ -503,6 +513,13 @@ int copy_context_skas0(unsigned long new_stack, int pid)
                 return err;
         }
 
+        err = put_fp_registers(pid, thread_fp_regs);
+        if (err < 0) {
+                printk(UM_KERN_ERR "copy_context_skas0 : put_fp_registers "
+                       "failed, pid = %d, err = %d\n", pid, err);
+                return err;
+        }
+
         /* set a well known return code for detection of child write failure */
         child_data->err = 12345678;
 
diff --git a/arch/um/sys-i386/shared/sysdep/ptrace.h b/arch/um/sys-i386/shared/sysdep/ptrace.h
index d50e62e07070..c398a5076111 100644
--- a/arch/um/sys-i386/shared/sysdep/ptrace.h
+++ b/arch/um/sys-i386/shared/sysdep/ptrace.h
@@ -53,6 +53,7 @@ extern int sysemu_supported;
 
 struct uml_pt_regs {
         unsigned long gp[MAX_REG_NR];
+        unsigned long fp[HOST_FPX_SIZE];
         struct faultinfo faultinfo;
         long syscall;
         int is_user;
diff --git a/arch/um/sys-x86_64/shared/sysdep/ptrace.h b/arch/um/sys-x86_64/shared/sysdep/ptrace.h
index fdba5457947a..8ee8f8e12af1 100644
--- a/arch/um/sys-x86_64/shared/sysdep/ptrace.h
+++ b/arch/um/sys-x86_64/shared/sysdep/ptrace.h
@@ -85,6 +85,7 @@
 
 struct uml_pt_regs {
         unsigned long gp[MAX_REG_NR];
+        unsigned long fp[HOST_FP_SIZE];
         struct faultinfo faultinfo;
         long syscall;
         int is_user;