The save_fp_context()/restore_fp_context() might sleep on accessing
user stack and therefore might lose FPU ownership in middle of them.
If these function failed due to "in_atomic" test in do_page_fault,
touch the sigcontext area in non-atomic context and retry these
save/restore operation.
This is a replacement of a (broken) fix which was titled "Allow CpU
exception in kernel partially".
Signed-off-by: Atsushi Nemoto <anemo@xxxxxxxxxxxxx>
---
This patch depends on:
> Subject: Re: [PATCH] Disallow CpU exception in kernel again.
> Message-Id: <20070414.023726.128617751.anemo@xxxxxxxxxxxxx>
arch/mips/kernel/signal-common.h | 9 ++++++
arch/mips/kernel/signal.c | 52 +++++++++++++++++++++++++++++++------
arch/mips/kernel/signal32.c | 52 +++++++++++++++++++++++++++++++------
include/asm-mips/fpu.h | 9 +++++-
4 files changed, 102 insertions(+), 20 deletions(-)
diff --git a/arch/mips/kernel/signal-common.h b/arch/mips/kernel/signal-common.h
index 297dfcb..c0faabd 100644
--- a/arch/mips/kernel/signal-common.h
+++ b/arch/mips/kernel/signal-common.h
@@ -34,4 +34,13 @@ extern int install_sigtramp(unsigned int
/* Check and clear pending FPU exceptions in saved CSR */
extern int fpcsr_pending(unsigned int __user *fpcsr);
+/* Make sure we will not lose FPU ownership */
+#ifdef CONFIG_PREEMPT
+#define lock_fpu_owner() preempt_disable()
+#define unlock_fpu_owner() preempt_enable()
+#else
+#define lock_fpu_owner() pagefault_disable()
+#define unlock_fpu_owner() pagefault_enable()
+#endif
+
#endif /* __SIGNAL_COMMON_H */
diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index fa58119..07d6730 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -20,6 +20,7 @@
#include <linux/ptrace.h>
#include <linux/unistd.h>
#include <linux/compiler.h>
+#include <linux/uaccess.h>
#include <asm/abi.h>
#include <asm/asm.h>
@@ -27,7 +28,6 @@
#include <asm/cacheflush.h>
#include <asm/fpu.h>
#include <asm/sim.h>
-#include <asm/uaccess.h>
#include <asm/ucontext.h>
#include <asm/cpu-features.h>
#include <asm/war.h>
@@ -78,6 +78,46 @@ struct rt_sigframe {
/*
* Helper routines
*/
+static int protected_save_fp_context(struct sigcontext __user *sc)
+{
+ int err;
+ while (1) {
+ lock_fpu_owner();
+ own_fpu_inatomic(1);
+ err = save_fp_context(sc); /* this might fail */
+ unlock_fpu_owner();
+ if (likely(!err))
+ break;
+ /* touch the sigcontext and try again */
+ err = __put_user(0, &sc->sc_fpregs[0]) |
+ __put_user(0, &sc->sc_fpregs[31]) |
+ __put_user(0, &sc->sc_fpc_csr);
+ if (err)
+ break; /* really bad sigcontext */
+ }
+ return err;
+}
+
+static int protected_restore_fp_context(struct sigcontext __user *sc)
+{
+ int err, tmp;
+ while (1) {
+ lock_fpu_owner();
+ own_fpu_inatomic(0);
+ err = restore_fp_context(sc); /* this might fail */
+ unlock_fpu_owner();
+ if (likely(!err))
+ break;
+ /* touch the sigcontext and try again */
+ err = __get_user(tmp, &sc->sc_fpregs[0]) |
+ __get_user(tmp, &sc->sc_fpregs[31]) |
+ __get_user(tmp, &sc->sc_fpc_csr);
+ if (err)
+ break; /* really bad sigcontext */
+ }
+ return err;
+}
+
int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
{
int err = 0;
@@ -113,10 +153,7 @@ int setup_sigcontext(struct pt_regs *reg
* Save FPU state to signal context. Signal handler
* will "inherit" current FPU state.
*/
- preempt_disable();
- own_fpu(1);
- err |= save_fp_context(sc);
- preempt_enable();
+ err |= protected_save_fp_context(sc);
}
return err;
}
@@ -148,10 +185,7 @@ check_and_restore_fp_context(struct sigc
err = sig = fpcsr_pending(&sc->sc_fpc_csr);
if (err > 0)
err = 0;
- preempt_disable();
- own_fpu(0);
- err |= restore_fp_context(sc);
- preempt_enable();
+ err |= protected_restore_fp_context(sc);
return err ?: sig;
}
diff --git a/arch/mips/kernel/signal32.c b/arch/mips/kernel/signal32.c
index 53a337c..b9a0144 100644
--- a/arch/mips/kernel/signal32.c
+++ b/arch/mips/kernel/signal32.c
@@ -22,6 +22,7 @@
#include <linux/compat.h>
#include <linux/suspend.h>
#include <linux/compiler.h>
+#include <linux/uaccess.h>
#include <asm/abi.h>
#include <asm/asm.h>
@@ -29,7 +30,6 @@
#include <linux/bitops.h>
#include <asm/cacheflush.h>
#include <asm/sim.h>
-#include <asm/uaccess.h>
#include <asm/ucontext.h>
#include <asm/system.h>
#include <asm/fpu.h>
@@ -176,6 +176,46 @@ struct rt_sigframe32 {
/*
* sigcontext handlers
*/
+static int protected_save_fp_context32(struct sigcontext32 __user *sc)
+{
+ int err;
+ while (1) {
+ lock_fpu_owner();
+ own_fpu_inatomic(1);
+ err = save_fp_context32(sc); /* this might fail */
+ unlock_fpu_owner();
+ if (likely(!err))
+ break;
+ /* touch the sigcontext and try again */
+ err = __put_user(0, &sc->sc_fpregs[0]) |
+ __put_user(0, &sc->sc_fpregs[31]) |
+ __put_user(0, &sc->sc_fpc_csr);
+ if (err)
+ break; /* really bad sigcontext */
+ }
+ return err;
+}
+
+static int protected_restore_fp_context32(struct sigcontext32 __user *sc)
+{
+ int err, tmp;
+ while (1) {
+ lock_fpu_owner();
+ own_fpu_inatomic(0);
+ err = restore_fp_context32(sc); /* this might fail */
+ unlock_fpu_owner();
+ if (likely(!err))
+ break;
+ /* touch the sigcontext and try again */
+ err = __get_user(tmp, &sc->sc_fpregs[0]) |
+ __get_user(tmp, &sc->sc_fpregs[31]) |
+ __get_user(tmp, &sc->sc_fpc_csr);
+ if (err)
+ break; /* really bad sigcontext */
+ }
+ return err;
+}
+
static int setup_sigcontext32(struct pt_regs *regs,
struct sigcontext32 __user *sc)
{
@@ -209,10 +249,7 @@ static int setup_sigcontext32(struct pt_
* Save FPU state to signal context. Signal handler
* will "inherit" current FPU state.
*/
- preempt_disable();
- own_fpu(1);
- err |= save_fp_context32(sc);
- preempt_enable();
+ err |= protected_save_fp_context32(sc);
}
return err;
}
@@ -225,10 +262,7 @@ check_and_restore_fp_context32(struct si
err = sig = fpcsr_pending(&sc->sc_fpc_csr);
if (err > 0)
err = 0;
- preempt_disable();
- own_fpu(0);
- err |= restore_fp_context32(sc);
- preempt_enable();
+ err |= protected_restore_fp_context32(sc);
return err ?: sig;
}
diff --git a/include/asm-mips/fpu.h b/include/asm-mips/fpu.h
index 71436f9..b414a7d 100644
--- a/include/asm-mips/fpu.h
+++ b/include/asm-mips/fpu.h
@@ -100,14 +100,19 @@ static inline void __own_fpu(void)
set_thread_flag(TIF_USEDFPU);
}
-static inline void own_fpu(int restore)
+static inline void own_fpu_inatomic(int restore)
{
- preempt_disable();
if (cpu_has_fpu && !__is_fpu_owner()) {
__own_fpu();
if (restore)
_restore_fp(current);
}
+}
+
+static inline void own_fpu(int restore)
+{
+ preempt_disable();
+ own_fpu_inatomic(restore);
preempt_enable();
}
