Re: [MIPS] Check FCSR for pending interrupts before restoring from a context.

[Atsushi Nemoto <anemo@mba.ocn.ne.jp>]

On Wed, 14 Feb 2007 17:04:20 +0900 (JST), Atsushi Nemoto <anemo@mba.ocn.ne.jp> 
wrote:
> Subject: Check FCSR for pending interrupts, alternative version
> 
> The commit 6d6671066a311703bca1b91645bb1e04cc983387 is incomplete and
> misses non-r4k CPUs.  This patch reverts the commit and fixes in other
> way.
> 
> * Do FCSR checking in caller of restore_fp_context.
> * Send SIGFPE if the signal handler set any FPU exception bits.

And this is for 2.6.20-stable tree.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
---
 arch/mips/kernel/r4k_fpu.S       |   16 --------------
 arch/mips/kernel/signal-common.h |   35 ++++++++++++++++++++++++++++++-
 arch/mips/kernel/signal.c        |   12 +++++++++-
 arch/mips/kernel/signal32.c      |   41 +++++++++++++++++++++++++++++++++++--
 arch/mips/kernel/signal_n32.c    |    6 ++++-
 5 files changed, 88 insertions(+), 22 deletions(-)

diff --git a/arch/mips/kernel/r4k_fpu.S b/arch/mips/kernel/r4k_fpu.S
index 59c1577..dbd42ad 100644
--- a/arch/mips/kernel/r4k_fpu.S
+++ b/arch/mips/kernel/r4k_fpu.S
@@ -114,14 +114,6 @@ LEAF(_save_fp_context32)
  */
 LEAF(_restore_fp_context)
        EX      lw t0, SC_FPC_CSR(a0)
-
-       /* Fail if the CSR has exceptions pending */
-       srl     t1, t0, 5
-       and     t1, t0
-       andi    t1, 0x1f << 7
-       bnez    t1, fault
-        nop
-
 #ifdef CONFIG_64BIT
        EX      ldc1 $f1, SC_FPREGS+8(a0)
        EX      ldc1 $f3, SC_FPREGS+24(a0)
@@ -165,14 +157,6 @@ LEAF(_restore_fp_context)
 LEAF(_restore_fp_context32)
        /* Restore an o32 sigcontext.  */
        EX      lw t0, SC32_FPC_CSR(a0)
-
-       /* Fail if the CSR has exceptions pending */
-       srl     t1, t0, 5
-       and     t1, t0
-       andi    t1, 0x1f << 7
-       bnez    t1, fault
-        nop
-
        EX      ldc1 $f0, SC32_FPREGS+0(a0)
        EX      ldc1 $f2, SC32_FPREGS+16(a0)
        EX      ldc1 $f4, SC32_FPREGS+32(a0)
diff --git a/arch/mips/kernel/signal-common.h b/arch/mips/kernel/signal-common.h
index b1f09d5..0811298 100644
--- a/arch/mips/kernel/signal-common.h
+++ b/arch/mips/kernel/signal-common.h
@@ -66,6 +66,38 @@ out:
 }
 
 static inline int
+fpcsr_pending(unsigned int __user *fpcsr)
+{
+       int err, sig = 0;
+       unsigned int csr, enabled;
+
+       err = __get_user(csr, fpcsr);
+       enabled = FPU_CSR_UNI_X | ((csr & FPU_CSR_ALL_E) << 5);
+       /*
+        * If the signal handler set some FPU exceptions, clear it and
+        * send SIGFPE.
+        */
+       if (csr & enabled) {
+               csr &= ~enabled;
+               err |= __put_user(csr, fpcsr);
+               sig = SIGFPE;
+       }
+       return err ?: sig;
+}
+
+static inline int
+check_and_restore_fp_context(struct sigcontext __user *sc)
+{
+       int err, sig;
+
+       err = sig = fpcsr_pending(&sc->sc_fpc_csr);
+       if (err > 0)
+               err = 0;
+       err |= restore_fp_context(sc);
+       return err ?: sig;
+}
+
+static inline int
 restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
 {
        unsigned int used_math;
@@ -112,7 +144,8 @@ restore_sigcontext(struct pt_regs *regs,
        if (used_math()) {
                /* restore fpu context if we have used it before */
                own_fpu();
-               err |= restore_fp_context(sc);
+               if (!err)
+                       err = check_and_restore_fp_context(sc);
        } else {
                /* signal handler may have used FPU.  Give it up. */
                lose_fpu();
diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index b9d358e..c19408e 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -190,6 +190,7 @@ _sys_sigreturn(nabi_no_regargs struct pt
 {
        struct sigframe __user *frame;
        sigset_t blocked;
+       int sig;
 
        frame = (struct sigframe __user *) regs.regs[29];
        if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
@@ -203,8 +204,11 @@ _sys_sigreturn(nabi_no_regargs struct pt
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);
 
-       if (restore_sigcontext(&regs, &frame->sf_sc))
+       sig = restore_sigcontext(&regs, &frame->sf_sc);
+       if (sig < 0)
                goto badframe;
+       else if (sig)
+               force_sig(sig, current);
 
        /*
         * Don't let your children do this ...
@@ -228,6 +232,7 @@ _sys_rt_sigreturn(nabi_no_regargs struct
        struct rt_sigframe __user *frame;
        sigset_t set;
        stack_t st;
+       int sig;
 
        frame = (struct rt_sigframe __user *) regs.regs[29];
        if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
@@ -241,8 +246,11 @@ _sys_rt_sigreturn(nabi_no_regargs struct
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);
 
-       if (restore_sigcontext(&regs, &frame->rs_uc.uc_mcontext))
+       sig = restore_sigcontext(&regs, &frame->rs_uc.uc_mcontext);
+       if (sig < 0)
                goto badframe;
+       else if (sig)
+               force_sig(sig, current);
 
        if (__copy_from_user(&st, &frame->rs_uc.uc_stack, sizeof(st)))
                goto badframe;
diff --git a/arch/mips/kernel/signal32.c b/arch/mips/kernel/signal32.c
index 7464df4..80ac070 100644
--- a/arch/mips/kernel/signal32.c
+++ b/arch/mips/kernel/signal32.c
@@ -321,6 +321,38 @@ asmlinkage int sys32_sigaltstack(nabi_no
        return ret;
 }
 
+static inline int
+fpcsr_pending(unsigned int __user *fpcsr)
+{
+       int err, sig = 0;
+       unsigned int csr, enabled;
+
+       err = __get_user(csr, fpcsr);
+       enabled = FPU_CSR_UNI_X | ((csr & FPU_CSR_ALL_E) << 5);
+       /*
+        * If the signal handler set some FPU exceptions, clear it and
+        * send SIGFPE.
+        */
+       if (csr & enabled) {
+               csr &= ~enabled;
+               err |= __put_user(csr, fpcsr);
+               sig = SIGFPE;
+       }
+       return err ?: sig;
+}
+
+static inline int
+check_and_restore_fp_context32(struct sigcontext32 __user *sc)
+{
+       int err, sig;
+
+       err = sig = fpcsr_pending(&sc->sc_fpc_csr);
+       if (err > 0)
+               err = 0;
+       err |= restore_fp_context32(sc);
+       return err ?: sig;
+}
+
 static int restore_sigcontext32(struct pt_regs *regs, struct sigcontext32 
__user *sc)
 {
        u32 used_math;
@@ -367,7 +399,8 @@ static int restore_sigcontext32(struct p
        if (used_math()) {
                /* restore fpu context if we have used it before */
                own_fpu();
-               err |= restore_fp_context32(sc);
+               if (!err)
+                       err = check_and_restore_fp_context32(sc);
        } else {
                /* signal handler may have used FPU.  Give it up. */
                lose_fpu();
@@ -464,6 +497,7 @@ _sys32_sigreturn(nabi_no_regargs struct
 {
        struct sigframe __user *frame;
        sigset_t blocked;
+       int sig;
 
        frame = (struct sigframe __user *) regs.regs[29];
        if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
@@ -477,8 +511,11 @@ _sys32_sigreturn(nabi_no_regargs struct
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);
 
-       if (restore_sigcontext32(&regs, &frame->sf_sc))
+       sig = restore_sigcontext32(&regs, &frame->sf_sc);
+       if (sig < 0)
                goto badframe;
+       else if (sig)
+               force_sig(sig, current);
 
        /*
         * Don't let your children do this ...
diff --git a/arch/mips/kernel/signal_n32.c b/arch/mips/kernel/signal_n32.c
index d6160c9..617edd9 100644
--- a/arch/mips/kernel/signal_n32.c
+++ b/arch/mips/kernel/signal_n32.c
@@ -123,6 +123,7 @@ _sysn32_rt_sigreturn(nabi_no_regargs str
        sigset_t set;
        stack_t st;
        s32 sp;
+       int sig;
 
        frame = (struct rt_sigframe_n32 __user *) regs.regs[29];
        if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
@@ -136,8 +137,11 @@ _sysn32_rt_sigreturn(nabi_no_regargs str
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);
 
-       if (restore_sigcontext(&regs, &frame->rs_uc.uc_mcontext))
+       sig = restore_sigcontext(&regs, &frame->rs_uc.uc_mcontext);
+       if (sig < 0)
                goto badframe;
+       else if (sig)
+               force_sig(sig, current);
 
        /* The ucontext contains a stack32_t, so we must convert!  */
        if (__get_user(sp, &frame->rs_uc.uc_stack.ss_sp))