[PATCH v4 00/10] Improve signal performance on PPC64 with KUAP

[PATCH v4 00/10] Improve signal performance on PPC64 with KUAP

[Christopher M. Riedl]

As reported by Anton, there is a large penalty to signal handling
performance on radix systems using KUAP. The signal handling code
performs many user access operations, each of which needs to switch the
KUAP permissions bit to open and then close user access. This involves a
costly 'mtspr' operation [0].

There is existing work done on x86 and by Christopher Leroy for PPC32 to
instead open up user access in "blocks" using user_*_access_{begin,end}.
We can do the same in PPC64 to bring performance back up on KUAP-enabled
radix and now also hash MMU systems [1].

Hash MMU KUAP support along with uaccess flush has landed in linuxppc/next
since the last revision. This series also provides a large benefit on hash
with KUAP. However, in the hash implementation of KUAP the user AMR is
always restored during system_call_exception() which cannot be avoided.
Fewer user access switches naturally also result in less uaccess flushing.

The first two patches add some needed 'unsafe' versions of copy-from
functions. While these do not make use of asm-goto they still allow for
avoiding the repeated uaccess switches.

The third patch moves functions called by setup_sigcontext() into a new
prepare_setup_sigcontext() to simplify converting setup_sigcontext()
into an 'unsafe' version which assumes an open uaccess window later.

The fourth and fifths patches clean-up some of the Transactional Memory
ifdef stuff to simplify using uaccess blocks later.

The next two patches rewrite some of the signal64 helper functions to
be 'unsafe'. Finally, the last three patches update the main signal
handling functions to make use of the new 'unsafe' helpers and eliminate
some additional uaccess switching.

I used the will-it-scale signal1 benchmark to measure and compare
performance [2]. The below results are from running a minimal
kernel+initramfs QEMU/KVM guest on a POWER9 Blackbird:

	signal1_threads -t1 -s10

	|                             | hash   | radix  |
	| --------------------------- | ------ | ------ |
	| linuxppc/next               | 118693 | 133296 |
	| linuxppc/next w/o KUAP+KUEP | 228911 | 228654 |
	| unsafe-signal64             | 199443 | 234716 |

[0]: https://github.com/linuxppc/issues/issues/277
[1]: https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=196278
[2]: https://github.com/antonblanchard/will-it-scale/blob/master/tests/signal1.c

v4:	* Fix issues identified by Christophe Leroy (thanks for review)
	* Use __get_user() directly to copy the 8B sigset_t

v3:	* Rebase on latest linuxppc/next
	* Reword confusing commit messages
	* Add missing comma in macro in signal.h which broke compiles without
	  CONFIG_ALTIVEC
	* Validate hash KUAP signal performance improvements

v2:	* Rebase on latest linuxppc/next + Christophe Leroy's PPC32
	  signal series
	* Simplify/remove TM ifdefery similar to PPC32 series and clean
	  up the uaccess begin/end calls
	* Isolate non-inline functions so they are not called when
	  uaccess window is open

Christopher M. Riedl (8):
  powerpc/uaccess: Add unsafe_copy_from_user
  powerpc/signal: Add unsafe_copy_{vsx,fpr}_from_user()
  powerpc/signal64: Move non-inline functions out of setup_sigcontext()
  powerpc: Reference param in MSR_TM_ACTIVE() macro
  powerpc/signal64: Remove TM ifdefery in middle of if/else block
  powerpc/signal64: Replace setup_sigcontext() w/
    unsafe_setup_sigcontext()
  powerpc/signal64: Replace restore_sigcontext() w/
    unsafe_restore_sigcontext()
  powerpc/signal64: Use __get_user() to copy sigset_t

Daniel Axtens (2):
  powerpc/signal64: Rewrite handle_rt_signal64() to minimise uaccess
    switches
  powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches

 arch/powerpc/include/asm/reg.h     |   2 +-
 arch/powerpc/include/asm/uaccess.h |   3 +
 arch/powerpc/kernel/signal.h       |  33 ++++
 arch/powerpc/kernel/signal_64.c    | 251 ++++++++++++++++++-----------
 4 files changed, 196 insertions(+), 93 deletions(-)

-- 
2.26.1

[PATCH v4 01/10] powerpc/uaccess: Add unsafe_copy_from_user

[Christopher M. Riedl]

Just wrap __copy_tofrom_user() for the usual 'unsafe' pattern which
takes in a label to goto on error.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/include/asm/uaccess.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 501c9a79038c..036e82eefac9 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -542,6 +542,9 @@ user_write_access_begin(const void __user *ptr, size_t len)
 #define unsafe_get_user(x, p, e) unsafe_op_wrap(__get_user_allowed(x, p), e)
 #define unsafe_put_user(x, p, e) __put_user_goto(x, p, e)
 
+#define unsafe_copy_from_user(d, s, l, e) \
+	unsafe_op_wrap(__copy_tofrom_user((__force void __user *)d, s, l), e)
+
 #define unsafe_copy_to_user(d, s, l, e) \
 do {									\
 	u8 __user *_dst = (u8 __user *)(d);				\
-- 
2.26.1

[PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Christopher M. Riedl]

Reuse the "safe" implementation from signal.c except for calling
unsafe_copy_from_user() to copy into a local buffer.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
index 2559a681536e..c18402d625f1 100644
--- a/arch/powerpc/kernel/signal.h
+++ b/arch/powerpc/kernel/signal.h
@@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
 				&buf[i], label);\
 } while (0)
 
+#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
+	struct task_struct *__t = task;					\
+	u64 __user *__f = (u64 __user *)from;				\
+	u64 buf[ELF_NFPREG];						\
+	int i;								\
+									\
+	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
+				label);					\
+	for (i = 0; i < ELF_NFPREG - 1; i++)				\
+		__t->thread.TS_FPR(i) = buf[i];				\
+	__t->thread.fp_state.fpscr = buf[i];				\
+} while (0)
+
+#define unsafe_copy_vsx_from_user(task, from, label)	do {		\
+	struct task_struct *__t = task;					\
+	u64 __user *__f = (u64 __user *)from;				\
+	u64 buf[ELF_NVSRHALFREG];					\
+	int i;								\
+									\
+	unsafe_copy_from_user(buf, __f,					\
+				ELF_NVSRHALFREG * sizeof(double),	\
+				label);					\
+	for (i = 0; i < ELF_NVSRHALFREG ; i++)				\
+		__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];	\
+} while (0)
+
+
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 #define unsafe_copy_ckfpr_to_user(to, task, label)	do {		\
 	struct task_struct *__t = task;					\
@@ -80,6 +107,10 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
 	unsafe_copy_to_user(to, (task)->thread.fp_state.fpr,	\
 			    ELF_NFPREG * sizeof(double), label)
 
+#define unsafe_copy_fpr_from_user(task, from, label)			\
+	unsafe_copy_from_user((task)->thread.fp_state.fpr, from,	\
+			    ELF_NFPREG * sizeof(double), label)
+
 static inline unsigned long
 copy_fpr_to_user(void __user *to, struct task_struct *task)
 {
@@ -115,6 +146,8 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
 #else
 #define unsafe_copy_fpr_to_user(to, task, label) do { } while (0)
 
+#define unsafe_copy_fpr_from_user(task, from, label) do { } while (0)
+
 static inline unsigned long
 copy_fpr_to_user(void __user *to, struct task_struct *task)
 {
-- 
2.26.1

[PATCH v4 03/10] powerpc/signal64: Move non-inline functions out of setup_sigcontext()

[Christopher M. Riedl]

There are non-inline functions which get called in setup_sigcontext() to
save register state to the thread struct. Move these functions into a
separate prepare_setup_sigcontext() function so that
setup_sigcontext() can be refactored later into an "unsafe" version
which assumes an open uaccess window. Non-inline functions should be
avoided when uaccess is open.

The majority of setup_sigcontext() can be refactored to execute in an
"unsafe" context (uaccess window is opened) except for some non-inline
functions. Move these out into a separate prepare_setup_sigcontext()
function which must be called first and before opening up a uaccess
window. A follow-up commit converts setup_sigcontext() to be "unsafe".

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index f9e4a1ac440f..b211a8ea4f6e 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -79,6 +79,24 @@ static elf_vrreg_t __user *sigcontext_vmx_regs(struct sigcontext __user *sc)
 }
 #endif
 
+static void prepare_setup_sigcontext(struct task_struct *tsk, int ctx_has_vsx_region)
+{
+#ifdef CONFIG_ALTIVEC
+	/* save altivec registers */
+	if (tsk->thread.used_vr)
+		flush_altivec_to_thread(tsk);
+	if (cpu_has_feature(CPU_FTR_ALTIVEC))
+		tsk->thread.vrsave = mfspr(SPRN_VRSAVE);
+#endif /* CONFIG_ALTIVEC */
+
+	flush_fp_to_thread(tsk);
+
+#ifdef CONFIG_VSX
+	if (tsk->thread.used_vsr && ctx_has_vsx_region)
+		flush_vsx_to_thread(tsk);
+#endif /* CONFIG_VSX */
+}
+
 /*
  * Set up the sigcontext for the signal frame.
  */
@@ -97,7 +115,6 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	 */
 #ifdef CONFIG_ALTIVEC
 	elf_vrreg_t __user *v_regs = sigcontext_vmx_regs(sc);
-	unsigned long vrsave;
 #endif
 	struct pt_regs *regs = tsk->thread.regs;
 	unsigned long msr = regs->msr;
@@ -112,7 +129,6 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 
 	/* save altivec registers */
 	if (tsk->thread.used_vr) {
-		flush_altivec_to_thread(tsk);
 		/* Copy 33 vec registers (vr0..31 and vscr) to the stack */
 		err |= __copy_to_user(v_regs, &tsk->thread.vr_state,
 				      33 * sizeof(vector128));
@@ -124,17 +140,10 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	/* We always copy to/from vrsave, it's 0 if we don't have or don't
 	 * use altivec.
 	 */
-	vrsave = 0;
-	if (cpu_has_feature(CPU_FTR_ALTIVEC)) {
-		vrsave = mfspr(SPRN_VRSAVE);
-		tsk->thread.vrsave = vrsave;
-	}
-
-	err |= __put_user(vrsave, (u32 __user *)&v_regs[33]);
+	err |= __put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);
 #else /* CONFIG_ALTIVEC */
 	err |= __put_user(0, &sc->v_regs);
 #endif /* CONFIG_ALTIVEC */
-	flush_fp_to_thread(tsk);
 	/* copy fpr regs and fpscr */
 	err |= copy_fpr_to_user(&sc->fp_regs, tsk);
 
@@ -150,7 +159,6 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	 * VMX data.
 	 */
 	if (tsk->thread.used_vsr && ctx_has_vsx_region) {
-		flush_vsx_to_thread(tsk);
 		v_regs += ELF_NVRREG;
 		err |= copy_vsx_to_user(v_regs, tsk);
 		/* set MSR_VSX in the MSR value in the frame to
@@ -655,6 +663,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 		ctx_has_vsx_region = 1;
 
 	if (old_ctx != NULL) {
+		prepare_setup_sigcontext(current, ctx_has_vsx_region);
 		if (!access_ok(old_ctx, ctx_size)
 		    || setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL, 0,
 					ctx_has_vsx_region)
@@ -842,6 +851,7 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 #endif
 	{
 		err |= __put_user(0, &frame->uc.uc_link);
+		prepare_setup_sigcontext(tsk, 1);
 		err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
 					NULL, (unsigned long)ksig->ka.sa.sa_handler,
 					1);
-- 
2.26.1

[PATCH v4 04/10] powerpc: Reference param in MSR_TM_ACTIVE() macro

[Christopher M. Riedl]

Unlike the other MSR_TM_* macros, MSR_TM_ACTIVE does not reference or
use its parameter unless CONFIG_PPC_TRANSACTIONAL_MEM is defined. This
causes an 'unused variable' compile warning unless the variable is also
guarded with CONFIG_PPC_TRANSACTIONAL_MEM.

Reference but do nothing with the argument in the macro to avoid a
potential compile warning.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/include/asm/reg.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index e40a921d78f9..c5a3e856191c 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -124,7 +124,7 @@
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 #define MSR_TM_ACTIVE(x) (((x) & MSR_TS_MASK) != 0) /* Transaction active? */
 #else
-#define MSR_TM_ACTIVE(x) 0
+#define MSR_TM_ACTIVE(x) ((void)(x), 0)
 #endif
 
 #if defined(CONFIG_PPC_BOOK3S_64)
-- 
2.26.1

[PATCH v4 05/10] powerpc/signal64: Remove TM ifdefery in middle of if/else block

[Christopher M. Riedl]

Rework the messy ifdef breaking up the if-else for TM similar to
commit f1cf4f93de2f ("powerpc/signal32: Remove ifdefery in middle of if/else").

Unlike that commit for ppc32, the ifdef can't be removed entirely since
uc_transact in sigframe depends on CONFIG_PPC_TRANSACTIONAL_MEM.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index b211a8ea4f6e..8e1d804ce552 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -710,9 +710,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	struct pt_regs *regs = current_pt_regs();
 	struct ucontext __user *uc = (struct ucontext __user *)regs->gpr[1];
 	sigset_t set;
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 	unsigned long msr;
-#endif
 
 	/* Always make any pending restarted system calls return -EINTR */
 	current->restart_block.fn = do_no_restart_syscall;
@@ -765,7 +763,10 @@ SYSCALL_DEFINE0(rt_sigreturn)
 
 	if (__get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR]))
 		goto badframe;
+#endif
+
 	if (MSR_TM_ACTIVE(msr)) {
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 		/* We recheckpoint on return. */
 		struct ucontext __user *uc_transact;
 
@@ -778,9 +779,8 @@ SYSCALL_DEFINE0(rt_sigreturn)
 		if (restore_tm_sigcontexts(current, &uc->uc_mcontext,
 					   &uc_transact->uc_mcontext))
 			goto badframe;
-	} else
 #endif
-	{
+	} else {
 		/*
 		 * Fall through, for non-TM restore
 		 *
@@ -818,10 +818,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 	unsigned long newsp = 0;
 	long err = 0;
 	struct pt_regs *regs = tsk->thread.regs;
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 	/* Save the thread's msr before get_tm_stackpointer() changes it */
 	unsigned long msr = regs->msr;
-#endif
 
 	frame = get_sigframe(ksig, tsk, sizeof(*frame), 0);
 	if (!access_ok(frame, sizeof(*frame)))
@@ -836,8 +834,9 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 	/* Create the ucontext.  */
 	err |= __put_user(0, &frame->uc.uc_flags);
 	err |= __save_altstack(&frame->uc.uc_stack, regs->gpr[1]);
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+
 	if (MSR_TM_ACTIVE(msr)) {
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 		/* The ucontext_t passed to userland points to the second
 		 * ucontext_t (for transactional state) with its uc_link ptr.
 		 */
@@ -847,9 +846,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 					    tsk, ksig->sig, NULL,
 					    (unsigned long)ksig->ka.sa.sa_handler,
 					    msr);
-	} else
 #endif
-	{
+	} else {
 		err |= __put_user(0, &frame->uc.uc_link);
 		prepare_setup_sigcontext(tsk, 1);
 		err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
-- 
2.26.1

[PATCH v4 06/10] powerpc/signal64: Replace setup_sigcontext() w/ unsafe_setup_sigcontext()

[Christopher M. Riedl]

Previously setup_sigcontext() performed a costly KUAP switch on every
uaccess operation. These repeated uaccess switches cause a significant
drop in signal handling performance.

Rewrite setup_sigcontext() to assume that a userspace write access window
is open. Replace all uaccess functions with their 'unsafe' versions
which avoid the repeated uaccess switches.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 70 ++++++++++++++++++++-------------
 1 file changed, 43 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 8e1d804ce552..4248e4489ff1 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -101,9 +101,13 @@ static void prepare_setup_sigcontext(struct task_struct *tsk, int ctx_has_vsx_re
  * Set up the sigcontext for the signal frame.
  */
 
-static long setup_sigcontext(struct sigcontext __user *sc,
-		struct task_struct *tsk, int signr, sigset_t *set,
-		unsigned long handler, int ctx_has_vsx_region)
+#define unsafe_setup_sigcontext(sc, tsk, signr, set, handler,		\
+				ctx_has_vsx_region, e)			\
+	unsafe_op_wrap(__unsafe_setup_sigcontext(sc, tsk, signr, set,	\
+			handler, ctx_has_vsx_region), e)
+static long notrace __unsafe_setup_sigcontext(struct sigcontext __user *sc,
+					struct task_struct *tsk, int signr, sigset_t *set,
+					unsigned long handler, int ctx_has_vsx_region)
 {
 	/* When CONFIG_ALTIVEC is set, we _always_ setup v_regs even if the
 	 * process never used altivec yet (MSR_VEC is zero in pt_regs of
@@ -118,20 +122,19 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 #endif
 	struct pt_regs *regs = tsk->thread.regs;
 	unsigned long msr = regs->msr;
-	long err = 0;
 	/* Force usr to alway see softe as 1 (interrupts enabled) */
 	unsigned long softe = 0x1;
 
 	BUG_ON(tsk != current);
 
 #ifdef CONFIG_ALTIVEC
-	err |= __put_user(v_regs, &sc->v_regs);
+	unsafe_put_user(v_regs, &sc->v_regs, efault_out);
 
 	/* save altivec registers */
 	if (tsk->thread.used_vr) {
 		/* Copy 33 vec registers (vr0..31 and vscr) to the stack */
-		err |= __copy_to_user(v_regs, &tsk->thread.vr_state,
-				      33 * sizeof(vector128));
+		unsafe_copy_to_user(v_regs, &tsk->thread.vr_state,
+				    33 * sizeof(vector128), efault_out);
 		/* set MSR_VEC in the MSR value in the frame to indicate that sc->v_reg)
 		 * contains valid data.
 		 */
@@ -140,12 +143,12 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	/* We always copy to/from vrsave, it's 0 if we don't have or don't
 	 * use altivec.
 	 */
-	err |= __put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);
+	unsafe_put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33], efault_out);
 #else /* CONFIG_ALTIVEC */
-	err |= __put_user(0, &sc->v_regs);
+	unsafe_put_user(0, &sc->v_regs, efault_out);
 #endif /* CONFIG_ALTIVEC */
 	/* copy fpr regs and fpscr */
-	err |= copy_fpr_to_user(&sc->fp_regs, tsk);
+	unsafe_copy_fpr_to_user(&sc->fp_regs, tsk, efault_out);
 
 	/*
 	 * Clear the MSR VSX bit to indicate there is no valid state attached
@@ -160,24 +163,27 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	 */
 	if (tsk->thread.used_vsr && ctx_has_vsx_region) {
 		v_regs += ELF_NVRREG;
-		err |= copy_vsx_to_user(v_regs, tsk);
+		unsafe_copy_vsx_to_user(v_regs, tsk, efault_out);
 		/* set MSR_VSX in the MSR value in the frame to
 		 * indicate that sc->vs_reg) contains valid data.
 		 */
 		msr |= MSR_VSX;
 	}
 #endif /* CONFIG_VSX */
-	err |= __put_user(&sc->gp_regs, &sc->regs);
+	unsafe_put_user(&sc->gp_regs, &sc->regs, efault_out);
 	WARN_ON(!FULL_REGS(regs));
-	err |= __copy_to_user(&sc->gp_regs, regs, GP_REGS_SIZE);
-	err |= __put_user(msr, &sc->gp_regs[PT_MSR]);
-	err |= __put_user(softe, &sc->gp_regs[PT_SOFTE]);
-	err |= __put_user(signr, &sc->signal);
-	err |= __put_user(handler, &sc->handler);
+	unsafe_copy_to_user(&sc->gp_regs, regs, GP_REGS_SIZE, efault_out);
+	unsafe_put_user(msr, &sc->gp_regs[PT_MSR], efault_out);
+	unsafe_put_user(softe, &sc->gp_regs[PT_SOFTE], efault_out);
+	unsafe_put_user(signr, &sc->signal, efault_out);
+	unsafe_put_user(handler, &sc->handler, efault_out);
 	if (set != NULL)
-		err |=  __put_user(set->sig[0], &sc->oldmask);
+		unsafe_put_user(set->sig[0], &sc->oldmask, efault_out);
 
-	return err;
+	return 0;
+
+efault_out:
+	return -EFAULT;
 }
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
@@ -664,12 +670,15 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 
 	if (old_ctx != NULL) {
 		prepare_setup_sigcontext(current, ctx_has_vsx_region);
-		if (!access_ok(old_ctx, ctx_size)
-		    || setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL, 0,
-					ctx_has_vsx_region)
-		    || __copy_to_user(&old_ctx->uc_sigmask,
-				      &current->blocked, sizeof(sigset_t)))
+		if (!user_write_access_begin(old_ctx, ctx_size))
 			return -EFAULT;
+
+		unsafe_setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL,
+					0, ctx_has_vsx_region, efault_out);
+		unsafe_copy_to_user(&old_ctx->uc_sigmask, &current->blocked,
+				    sizeof(sigset_t), efault_out);
+
+		user_write_access_end();
 	}
 	if (new_ctx == NULL)
 		return 0;
@@ -698,6 +707,10 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	/* This returns like rt_sigreturn */
 	set_thread_flag(TIF_RESTOREALL);
 	return 0;
+
+efault_out:
+	user_write_access_end();
+	return -EFAULT;
 }
 
 
@@ -850,9 +863,12 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 	} else {
 		err |= __put_user(0, &frame->uc.uc_link);
 		prepare_setup_sigcontext(tsk, 1);
-		err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
-					NULL, (unsigned long)ksig->ka.sa.sa_handler,
-					1);
+		if (!user_write_access_begin(frame, sizeof(struct rt_sigframe)))
+			return -EFAULT;
+		err |= __unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk,
+						ksig->sig, NULL,
+						(unsigned long)ksig->ka.sa.sa_handler, 1);
+		user_write_access_end();
 	}
 	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 	if (err)
-- 
2.26.1

[PATCH v4 07/10] powerpc/signal64: Replace restore_sigcontext() w/ unsafe_restore_sigcontext()

[Christopher M. Riedl]

Previously restore_sigcontext() performed a costly KUAP switch on every
uaccess operation. These repeated uaccess switches cause a significant
drop in signal handling performance.

Rewrite restore_sigcontext() to assume that a userspace read access
window is open. Replace all uaccess functions with their 'unsafe'
versions which avoid the repeated uaccess switches.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 68 ++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 4248e4489ff1..d668f8af18fe 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -326,14 +326,14 @@ static long setup_tm_sigcontexts(struct sigcontext __user *sc,
 /*
  * Restore the sigcontext from the signal frame.
  */
-
-static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
-			      struct sigcontext __user *sc)
+#define unsafe_restore_sigcontext(tsk, set, sig, sc, e) \
+	unsafe_op_wrap(__unsafe_restore_sigcontext(tsk, set, sig, sc), e)
+static long notrace __unsafe_restore_sigcontext(struct task_struct *tsk, sigset_t *set,
+						int sig, struct sigcontext __user *sc)
 {
 #ifdef CONFIG_ALTIVEC
 	elf_vrreg_t __user *v_regs;
 #endif
-	unsigned long err = 0;
 	unsigned long save_r13 = 0;
 	unsigned long msr;
 	struct pt_regs *regs = tsk->thread.regs;
@@ -348,27 +348,28 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
 		save_r13 = regs->gpr[13];
 
 	/* copy the GPRs */
-	err |= __copy_from_user(regs->gpr, sc->gp_regs, sizeof(regs->gpr));
-	err |= __get_user(regs->nip, &sc->gp_regs[PT_NIP]);
+	unsafe_copy_from_user(regs->gpr, sc->gp_regs, sizeof(regs->gpr),
+			      efault_out);
+	unsafe_get_user(regs->nip, &sc->gp_regs[PT_NIP], efault_out);
 	/* get MSR separately, transfer the LE bit if doing signal return */
-	err |= __get_user(msr, &sc->gp_regs[PT_MSR]);
+	unsafe_get_user(msr, &sc->gp_regs[PT_MSR], efault_out);
 	if (sig)
 		regs->msr = (regs->msr & ~MSR_LE) | (msr & MSR_LE);
-	err |= __get_user(regs->orig_gpr3, &sc->gp_regs[PT_ORIG_R3]);
-	err |= __get_user(regs->ctr, &sc->gp_regs[PT_CTR]);
-	err |= __get_user(regs->link, &sc->gp_regs[PT_LNK]);
-	err |= __get_user(regs->xer, &sc->gp_regs[PT_XER]);
-	err |= __get_user(regs->ccr, &sc->gp_regs[PT_CCR]);
+	unsafe_get_user(regs->orig_gpr3, &sc->gp_regs[PT_ORIG_R3], efault_out);
+	unsafe_get_user(regs->ctr, &sc->gp_regs[PT_CTR], efault_out);
+	unsafe_get_user(regs->link, &sc->gp_regs[PT_LNK], efault_out);
+	unsafe_get_user(regs->xer, &sc->gp_regs[PT_XER], efault_out);
+	unsafe_get_user(regs->ccr, &sc->gp_regs[PT_CCR], efault_out);
 	/* Don't allow userspace to set SOFTE */
 	set_trap_norestart(regs);
-	err |= __get_user(regs->dar, &sc->gp_regs[PT_DAR]);
-	err |= __get_user(regs->dsisr, &sc->gp_regs[PT_DSISR]);
-	err |= __get_user(regs->result, &sc->gp_regs[PT_RESULT]);
+	unsafe_get_user(regs->dar, &sc->gp_regs[PT_DAR], efault_out);
+	unsafe_get_user(regs->dsisr, &sc->gp_regs[PT_DSISR], efault_out);
+	unsafe_get_user(regs->result, &sc->gp_regs[PT_RESULT], efault_out);
 
 	if (!sig)
 		regs->gpr[13] = save_r13;
 	if (set != NULL)
-		err |=  __get_user(set->sig[0], &sc->oldmask);
+		unsafe_get_user(set->sig[0], &sc->oldmask, efault_out);
 
 	/*
 	 * Force reload of FP/VEC.
@@ -378,29 +379,28 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
 	regs->msr &= ~(MSR_FP | MSR_FE0 | MSR_FE1 | MSR_VEC | MSR_VSX);
 
 #ifdef CONFIG_ALTIVEC
-	err |= __get_user(v_regs, &sc->v_regs);
-	if (err)
-		return err;
+	unsafe_get_user(v_regs, &sc->v_regs, efault_out);
 	if (v_regs && !access_ok(v_regs, 34 * sizeof(vector128)))
 		return -EFAULT;
 	/* Copy 33 vec registers (vr0..31 and vscr) from the stack */
 	if (v_regs != NULL && (msr & MSR_VEC) != 0) {
-		err |= __copy_from_user(&tsk->thread.vr_state, v_regs,
-					33 * sizeof(vector128));
+		unsafe_copy_from_user(&tsk->thread.vr_state, v_regs,
+				      33 * sizeof(vector128), efault_out);
 		tsk->thread.used_vr = true;
 	} else if (tsk->thread.used_vr) {
 		memset(&tsk->thread.vr_state, 0, 33 * sizeof(vector128));
 	}
 	/* Always get VRSAVE back */
 	if (v_regs != NULL)
-		err |= __get_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);
+		unsafe_get_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33],
+				efault_out);
 	else
 		tsk->thread.vrsave = 0;
 	if (cpu_has_feature(CPU_FTR_ALTIVEC))
 		mtspr(SPRN_VRSAVE, tsk->thread.vrsave);
 #endif /* CONFIG_ALTIVEC */
 	/* restore floating point */
-	err |= copy_fpr_from_user(tsk, &sc->fp_regs);
+	unsafe_copy_fpr_from_user(tsk, &sc->fp_regs, efault_out);
 #ifdef CONFIG_VSX
 	/*
 	 * Get additional VSX data. Update v_regs to point after the
@@ -409,14 +409,17 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
 	 */
 	v_regs += ELF_NVRREG;
 	if ((msr & MSR_VSX) != 0) {
-		err |= copy_vsx_from_user(tsk, v_regs);
+		unsafe_copy_vsx_from_user(tsk, v_regs, efault_out);
 		tsk->thread.used_vsr = true;
 	} else {
 		for (i = 0; i < 32 ; i++)
 			tsk->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = 0;
 	}
 #endif
-	return err;
+	return 0;
+
+efault_out:
+	return -EFAULT;
 }
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
@@ -701,8 +704,14 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	if (__copy_from_user(&set, &new_ctx->uc_sigmask, sizeof(set)))
 		do_exit(SIGSEGV);
 	set_current_blocked(&set);
-	if (restore_sigcontext(current, NULL, 0, &new_ctx->uc_mcontext))
+
+	if (!user_read_access_begin(new_ctx, ctx_size))
+		return -EFAULT;
+	if (__unsafe_restore_sigcontext(current, NULL, 0, &new_ctx->uc_mcontext)) {
+		user_read_access_end();
 		do_exit(SIGSEGV);
+	}
+	user_read_access_end();
 
 	/* This returns like rt_sigreturn */
 	set_thread_flag(TIF_RESTOREALL);
@@ -807,8 +816,13 @@ SYSCALL_DEFINE0(rt_sigreturn)
 		 * causing a TM bad thing.
 		 */
 		current->thread.regs->msr &= ~MSR_TS_MASK;
-		if (restore_sigcontext(current, NULL, 1, &uc->uc_mcontext))
+		if (!user_read_access_begin(uc, sizeof(*uc)))
+			return -EFAULT;
+		if (__unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext)) {
+			user_read_access_end();
 			goto badframe;
+		}
+		user_read_access_end();
 	}
 
 	if (restore_altstack(&uc->uc_stack))
-- 
2.26.1

[PATCH v4 08/10] powerpc/signal64: Rewrite handle_rt_signal64() to minimise uaccess switches

[Christopher M. Riedl]

From: Daniel Axtens <dja@axtens.net>

Add uaccess blocks and use the 'unsafe' versions of functions doing user
access where possible to reduce the number of times uaccess has to be
opened/closed.

There is no 'unsafe' version of copy_siginfo_to_user, so move it
slightly to allow for a "longer" uaccess block.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 54 +++++++++++++++++++++------------
 1 file changed, 34 insertions(+), 20 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index d668f8af18fe..a471e97589a8 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -849,44 +849,51 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 	unsigned long msr = regs->msr;
 
 	frame = get_sigframe(ksig, tsk, sizeof(*frame), 0);
-	if (!access_ok(frame, sizeof(*frame)))
-		goto badframe;
 
-	err |= __put_user(&frame->info, &frame->pinfo);
-	err |= __put_user(&frame->uc, &frame->puc);
-	err |= copy_siginfo_to_user(&frame->info, &ksig->info);
-	if (err)
+	/* This only applies when calling unsafe_setup_sigcontext() and must be
+	 * called before opening the uaccess window.
+	 */
+	if (!MSR_TM_ACTIVE(msr))
+		prepare_setup_sigcontext(tsk, 1);
+
+	if (!user_write_access_begin(frame, sizeof(*frame)))
 		goto badframe;
 
+	unsafe_put_user(&frame->info, &frame->pinfo, badframe_block);
+	unsafe_put_user(&frame->uc, &frame->puc, badframe_block);
+
 	/* Create the ucontext.  */
-	err |= __put_user(0, &frame->uc.uc_flags);
-	err |= __save_altstack(&frame->uc.uc_stack, regs->gpr[1]);
+	unsafe_put_user(0, &frame->uc.uc_flags, badframe_block);
+	unsafe_save_altstack(&frame->uc.uc_stack, regs->gpr[1], badframe_block);
 
 	if (MSR_TM_ACTIVE(msr)) {
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 		/* The ucontext_t passed to userland points to the second
 		 * ucontext_t (for transactional state) with its uc_link ptr.
 		 */
-		err |= __put_user(&frame->uc_transact, &frame->uc.uc_link);
+		unsafe_put_user(&frame->uc_transact, &frame->uc.uc_link, badframe_block);
+
+		user_write_access_end();
+
 		err |= setup_tm_sigcontexts(&frame->uc.uc_mcontext,
 					    &frame->uc_transact.uc_mcontext,
 					    tsk, ksig->sig, NULL,
 					    (unsigned long)ksig->ka.sa.sa_handler,
 					    msr);
+
+		if (!user_write_access_begin(frame, sizeof(struct rt_sigframe)))
+			goto badframe;
+
 #endif
 	} else {
-		err |= __put_user(0, &frame->uc.uc_link);
-		prepare_setup_sigcontext(tsk, 1);
-		if (!user_write_access_begin(frame, sizeof(struct rt_sigframe)))
-			return -EFAULT;
-		err |= __unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk,
-						ksig->sig, NULL,
-						(unsigned long)ksig->ka.sa.sa_handler, 1);
-		user_write_access_end();
+		unsafe_put_user(0, &frame->uc.uc_link, badframe_block);
+		unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
+					NULL, (unsigned long)ksig->ka.sa.sa_handler,
+					1, badframe_block);
 	}
-	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
-	if (err)
-		goto badframe;
+
+	unsafe_copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set), badframe_block);
+	user_write_access_end();
 
 	/* Make sure signal handler doesn't get spurious FP exceptions */
 	tsk->thread.fp_state.fpscr = 0;
@@ -901,6 +908,11 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 		regs->nip = (unsigned long) &frame->tramp[0];
 	}
 
+
+	/* Save the siginfo outside of the unsafe block. */
+	if (copy_siginfo_to_user(&frame->info, &ksig->info))
+		goto badframe;
+
 	/* Allocate a dummy caller frame for the signal handler. */
 	newsp = ((unsigned long)frame) - __SIGNAL_FRAMESIZE;
 	err |= put_user(regs->gpr[1], (unsigned long __user *)newsp);
@@ -940,6 +952,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 
 	return 0;
 
+badframe_block:
+	user_write_access_end();
 badframe:
 	signal_fault(current, regs, "handle_rt_signal64", frame);
 
-- 
2.26.1

[PATCH v4 09/10] powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches

[Christopher M. Riedl]

From: Daniel Axtens <dja@axtens.net>

Add uaccess blocks and use the 'unsafe' versions of functions doing user
access where possible to reduce the number of times uaccess has to be
opened/closed.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index a471e97589a8..817b64e1e409 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -782,9 +782,13 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	 * restore_tm_sigcontexts.
 	 */
 	regs->msr &= ~MSR_TS_MASK;
+#endif
 
-	if (__get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR]))
+	if (!user_read_access_begin(uc, sizeof(*uc)))
 		goto badframe;
+
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+	unsafe_get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR], badframe_block);
 #endif
 
 	if (MSR_TM_ACTIVE(msr)) {
@@ -794,10 +798,12 @@ SYSCALL_DEFINE0(rt_sigreturn)
 
 		/* Trying to start TM on non TM system */
 		if (!cpu_has_feature(CPU_FTR_TM))
-			goto badframe;
+			goto badframe_block;
+
+		unsafe_get_user(uc_transact, &uc->uc_link, badframe_block);
+
+		user_read_access_end();
 
-		if (__get_user(uc_transact, &uc->uc_link))
-			goto badframe;
 		if (restore_tm_sigcontexts(current, &uc->uc_mcontext,
 					   &uc_transact->uc_mcontext))
 			goto badframe;
@@ -816,12 +822,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
 		 * causing a TM bad thing.
 		 */
 		current->thread.regs->msr &= ~MSR_TS_MASK;
-		if (!user_read_access_begin(uc, sizeof(*uc)))
-			return -EFAULT;
-		if (__unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext)) {
-			user_read_access_end();
-			goto badframe;
-		}
+		unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext,
+					  badframe_block);
+
 		user_read_access_end();
 	}
 
@@ -831,6 +834,8 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	set_thread_flag(TIF_RESTOREALL);
 	return 0;
 
+badframe_block:
+	user_read_access_end();
 badframe:
 	signal_fault(current, regs, "rt_sigreturn", uc);
 
-- 
2.26.1

[PATCH v4 10/10] powerpc/signal64: Use __get_user() to copy sigset_t

[Christopher M. Riedl]

Usually sigset_t is exactly 8B which is a "trivial" size and does not
warrant using __copy_from_user(). Use __get_user() directly in
anticipation of future work to remove the trivial size optimizations
from __copy_from_user(). Calling __get_user() also results in a small
boost to signal handling throughput here.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 817b64e1e409..42fdc4a7ff72 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -97,6 +97,14 @@ static void prepare_setup_sigcontext(struct task_struct *tsk, int ctx_has_vsx_re
 #endif /* CONFIG_VSX */
 }
 
+static inline int get_user_sigset(sigset_t *dst, const sigset_t *src)
+{
+	if (sizeof(sigset_t) <= 8)
+		return __get_user(dst->sig[0], &src->sig[0]);
+	else
+		return __copy_from_user(dst, src, sizeof(sigset_t));
+}
+
 /*
  * Set up the sigcontext for the signal frame.
  */
@@ -701,8 +709,9 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	 * We kill the task with a SIGSEGV in this situation.
 	 */
 
-	if (__copy_from_user(&set, &new_ctx->uc_sigmask, sizeof(set)))
+	if (get_user_sigset(&set, &new_ctx->uc_sigmask))
 		do_exit(SIGSEGV);
+
 	set_current_blocked(&set);
 
 	if (!user_read_access_begin(new_ctx, ctx_size))
@@ -740,8 +749,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	if (!access_ok(uc, sizeof(*uc)))
 		goto badframe;
 
-	if (__copy_from_user(&set, &uc->uc_sigmask, sizeof(set)))
+	if (get_user_sigset(&set, &uc->uc_sigmask))
 		goto badframe;
+
 	set_current_blocked(&set);
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
-- 
2.26.1

RE: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[David Laight]

From: Christopher M. Riedl
> Sent: 28 January 2021 04:04
> 
> Reuse the "safe" implementation from signal.c except for calling
> unsafe_copy_from_user() to copy into a local buffer.
> 
> Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> ---
>  arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> index 2559a681536e..c18402d625f1 100644
> --- a/arch/powerpc/kernel/signal.h
> +++ b/arch/powerpc/kernel/signal.h
> @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
>  				&buf[i], label);\
>  } while (0)
> 
> +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
> +	struct task_struct *__t = task;					\
> +	u64 __user *__f = (u64 __user *)from;				\
> +	u64 buf[ELF_NFPREG];						\

How big is that buffer?
Isn't is likely to be reasonably large compared to a reasonable
kernel stack frame.
Especially since this isn't even a leaf function.

> +	int i;								\
> +									\
> +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\

That really ought to be sizeof(buf).

	David


> +				label);					\
> +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> +		__t->thread.TS_FPR(i) = buf[i];				\
> +	__t->thread.fp_state.fpscr = buf[i];				\
> +} while (0)
> +
> +#define unsafe_copy_vsx_from_user(task, from, label)	do {		\
> +	struct task_struct *__t = task;					\
> +	u64 __user *__f = (u64 __user *)from;				\
> +	u64 buf[ELF_NVSRHALFREG];					\
> +	int i;								\
> +									\
> +	unsafe_copy_from_user(buf, __f,					\
> +				ELF_NVSRHALFREG * sizeof(double),	\
> +				label);					\
> +	for (i = 0; i < ELF_NVSRHALFREG ; i++)				\
> +		__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];	\
> +} while (0)
> +
> +
>  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
>  #define unsafe_copy_ckfpr_to_user(to, task, label)	do {		\
>  	struct task_struct *__t = task;					\
> @@ -80,6 +107,10 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
>  	unsafe_copy_to_user(to, (task)->thread.fp_state.fpr,	\
>  			    ELF_NFPREG * sizeof(double), label)
> 
> +#define unsafe_copy_fpr_from_user(task, from, label)			\
> +	unsafe_copy_from_user((task)->thread.fp_state.fpr, from,	\
> +			    ELF_NFPREG * sizeof(double), label)
> +
>  static inline unsigned long
>  copy_fpr_to_user(void __user *to, struct task_struct *task)
>  {
> @@ -115,6 +146,8 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
>  #else
>  #define unsafe_copy_fpr_to_user(to, task, label) do { } while (0)
> 
> +#define unsafe_copy_fpr_from_user(task, from, label) do { } while (0)
> +
>  static inline unsigned long
>  copy_fpr_to_user(void __user *to, struct task_struct *task)
>  {
> --
> 2.26.1

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Christophe Leroy]

Le 28/01/2021 à 11:38, David Laight a écrit :
> From: Christopher M. Riedl
>> Sent: 28 January 2021 04:04
>>
>> Reuse the "safe" implementation from signal.c except for calling
>> unsafe_copy_from_user() to copy into a local buffer.
>>
>> Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
>> ---
>>   arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
>>   1 file changed, 33 insertions(+)
>>
>> diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
>> index 2559a681536e..c18402d625f1 100644
>> --- a/arch/powerpc/kernel/signal.h
>> +++ b/arch/powerpc/kernel/signal.h
>> @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
>>   				&buf[i], label);\
>>   } while (0)
>>
>> +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
>> +	struct task_struct *__t = task;					\
>> +	u64 __user *__f = (u64 __user *)from;				\
>> +	u64 buf[ELF_NFPREG];						\
> 
> How big is that buffer?

#define ELF_NFPREG	33

So that's 264 bytes.

That's a bit big but still reasonable I think.

Christophe

> Isn't is likely to be reasonably large compared to a reasonable
> kernel stack frame.
> Especially since this isn't even a leaf function.
> 
>> +	int i;								\
>> +									\
>> +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
> 
> That really ought to be sizeof(buf).
> 
> 	David
> 
> 
>> +				label);					\
>> +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
>> +		__t->thread.TS_FPR(i) = buf[i];				\
>> +	__t->thread.fp_state.fpscr = buf[i];				\
>> +} while (0)
>> +
>> +#define unsafe_copy_vsx_from_user(task, from, label)	do {		\
>> +	struct task_struct *__t = task;					\
>> +	u64 __user *__f = (u64 __user *)from;				\
>> +	u64 buf[ELF_NVSRHALFREG];					\
>> +	int i;								\
>> +									\
>> +	unsafe_copy_from_user(buf, __f,					\
>> +				ELF_NVSRHALFREG * sizeof(double),	\
>> +				label);					\
>> +	for (i = 0; i < ELF_NVSRHALFREG ; i++)				\
>> +		__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];	\
>> +} while (0)
>> +
>> +
>>   #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
>>   #define unsafe_copy_ckfpr_to_user(to, task, label)	do {		\
>>   	struct task_struct *__t = task;					\
>> @@ -80,6 +107,10 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
>>   	unsafe_copy_to_user(to, (task)->thread.fp_state.fpr,	\
>>   			    ELF_NFPREG * sizeof(double), label)
>>
>> +#define unsafe_copy_fpr_from_user(task, from, label)			\
>> +	unsafe_copy_from_user((task)->thread.fp_state.fpr, from,	\
>> +			    ELF_NFPREG * sizeof(double), label)
>> +
>>   static inline unsigned long
>>   copy_fpr_to_user(void __user *to, struct task_struct *task)
>>   {
>> @@ -115,6 +146,8 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
>>   #else
>>   #define unsafe_copy_fpr_to_user(to, task, label) do { } while (0)
>>
>> +#define unsafe_copy_fpr_from_user(task, from, label) do { } while (0)
>> +
>>   static inline unsigned long
>>   copy_fpr_to_user(void __user *to, struct task_struct *task)
>>   {
>> --
>> 2.26.1
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 

RE: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Christopher M. Riedl]

On Thu Jan 28, 2021 at 4:38 AM CST, David Laight wrote:
> From: Christopher M. Riedl
> > Sent: 28 January 2021 04:04
> > 
> > Reuse the "safe" implementation from signal.c except for calling
> > unsafe_copy_from_user() to copy into a local buffer.
> > 
> > Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> > ---
> >  arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> > 
> > diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> > index 2559a681536e..c18402d625f1 100644
> > --- a/arch/powerpc/kernel/signal.h
> > +++ b/arch/powerpc/kernel/signal.h
> > @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
> >  				&buf[i], label);\
> >  } while (0)
> > 
> > +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
> > +	struct task_struct *__t = task;					\
> > +	u64 __user *__f = (u64 __user *)from;				\
> > +	u64 buf[ELF_NFPREG];						\
>
> How big is that buffer?
> Isn't is likely to be reasonably large compared to a reasonable
> kernel stack frame.
> Especially since this isn't even a leaf function.
>

I think Christophe answered this - I don't really have an opinion either
way. What would be a 'reasonable' kernel stack frame for reference?

> > +	int i;								\
> > +									\
> > +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
>
> That really ought to be sizeof(buf).
>

Agreed, I will fix this. Thanks!

> David
>
>
> > +				label);					\
> > +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> > +		__t->thread.TS_FPR(i) = buf[i];				\
> > +	__t->thread.fp_state.fpscr = buf[i];				\
> > +} while (0)
> > +
> > +#define unsafe_copy_vsx_from_user(task, from, label)	do {		\
> > +	struct task_struct *__t = task;					\
> > +	u64 __user *__f = (u64 __user *)from;				\
> > +	u64 buf[ELF_NVSRHALFREG];					\
> > +	int i;								\
> > +									\
> > +	unsafe_copy_from_user(buf, __f,					\
> > +				ELF_NVSRHALFREG * sizeof(double),	\
> > +				label);					\
> > +	for (i = 0; i < ELF_NVSRHALFREG ; i++)				\
> > +		__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];	\
> > +} while (0)
> > +
> > +
> >  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> >  #define unsafe_copy_ckfpr_to_user(to, task, label)	do {		\
> >  	struct task_struct *__t = task;					\
> > @@ -80,6 +107,10 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
> >  	unsafe_copy_to_user(to, (task)->thread.fp_state.fpr,	\
> >  			    ELF_NFPREG * sizeof(double), label)
> > 
> > +#define unsafe_copy_fpr_from_user(task, from, label)			\
> > +	unsafe_copy_from_user((task)->thread.fp_state.fpr, from,	\
> > +			    ELF_NFPREG * sizeof(double), label)
> > +
> >  static inline unsigned long
> >  copy_fpr_to_user(void __user *to, struct task_struct *task)
> >  {
> > @@ -115,6 +146,8 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
> >  #else
> >  #define unsafe_copy_fpr_to_user(to, task, label) do { } while (0)
> > 
> > +#define unsafe_copy_fpr_from_user(task, from, label) do { } while (0)
> > +
> >  static inline unsigned long
> >  copy_fpr_to_user(void __user *to, struct task_struct *task)
> >  {
> > --
> > 2.26.1
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
> MK1 1PT, UK
> Registration No: 1397386 (Wales)

RE: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[David Laight]

From: Christopher M. Riedl
> Sent: 01 February 2021 15:56
> 
> On Thu Jan 28, 2021 at 4:38 AM CST, David Laight wrote:
> > From: Christopher M. Riedl
> > > Sent: 28 January 2021 04:04
> > >
> > > Reuse the "safe" implementation from signal.c except for calling
> > > unsafe_copy_from_user() to copy into a local buffer.
> > >
> > > Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> > > ---
> > >  arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
> > >  1 file changed, 33 insertions(+)
> > >
> > > diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> > > index 2559a681536e..c18402d625f1 100644
> > > --- a/arch/powerpc/kernel/signal.h
> > > +++ b/arch/powerpc/kernel/signal.h
> > > @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
> > >  				&buf[i], label);\
> > >  } while (0)
> > >
> > > +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
> > > +	struct task_struct *__t = task;					\
> > > +	u64 __user *__f = (u64 __user *)from;				\
> > > +	u64 buf[ELF_NFPREG];						\
> >
> > How big is that buffer?
> > Isn't is likely to be reasonably large compared to a reasonable
> > kernel stack frame.
> > Especially since this isn't even a leaf function.
> >
> 
> I think Christophe answered this - I don't really have an opinion either
> way. What would be a 'reasonable' kernel stack frame for reference?

Zero :-)

> 
> > > +	int i;								\
> > > +									\
> > > +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
> > > +				label);					\
> > > +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> > > +		__t->thread.TS_FPR(i) = buf[i];				\
> > > +	__t->thread.fp_state.fpscr = buf[i];				\
> > > +} while (0)

On further reflection, since you immediately loop through the buffer
why not just use user_access_begin() and unsafe_get_user() in the loop.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Gabriel Paubert]

On Mon, Feb 01, 2021 at 09:55:44AM -0600, Christopher M. Riedl wrote:
> On Thu Jan 28, 2021 at 4:38 AM CST, David Laight wrote:
> > From: Christopher M. Riedl
> > > Sent: 28 January 2021 04:04
> > > 
> > > Reuse the "safe" implementation from signal.c except for calling
> > > unsafe_copy_from_user() to copy into a local buffer.
> > > 
> > > Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> > > ---
> > >  arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
> > >  1 file changed, 33 insertions(+)
> > > 
> > > diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> > > index 2559a681536e..c18402d625f1 100644
> > > --- a/arch/powerpc/kernel/signal.h
> > > +++ b/arch/powerpc/kernel/signal.h
> > > @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
> > >  				&buf[i], label);\
> > >  } while (0)
> > > 
> > > +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
> > > +	struct task_struct *__t = task;					\
> > > +	u64 __user *__f = (u64 __user *)from;				\
> > > +	u64 buf[ELF_NFPREG];						\
> >
> > How big is that buffer?
> > Isn't is likely to be reasonably large compared to a reasonable
> > kernel stack frame.
> > Especially since this isn't even a leaf function.
> >
> 
> I think Christophe answered this - I don't really have an opinion either
> way. What would be a 'reasonable' kernel stack frame for reference?

See include/linux/poll.h, where the limit is of the order of 800 bytes
and the number of entries in an on stack array is chosen at compile time
(different between 32 and 64 bit for example).

The values are used in do_sys_poll, which, with almost 1000 bytes of
stack footprint, appears close to the top of "make checkstack". In
addition do_sys_poll has to call the ->poll function of every file
descriptor in its table, so it is not a tail function.

This 264 bytes array looks reasonable, but please use 'make checkstack'
to verify that the function's total stack usage stays within reason.

	Gabriel

> 
> > > +	int i;								\
> > > +									\
> > > +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
> >
> > That really ought to be sizeof(buf).
> >
> 
> Agreed, I will fix this. Thanks!
> 
> > David
> >
> >
> > > +				label);					\
> > > +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> > > +		__t->thread.TS_FPR(i) = buf[i];				\
> > > +	__t->thread.fp_state.fpscr = buf[i];				\
> > > +} while (0)
> > > +
> > > +#define unsafe_copy_vsx_from_user(task, from, label)	do {		\
> > > +	struct task_struct *__t = task;					\
> > > +	u64 __user *__f = (u64 __user *)from;				\
> > > +	u64 buf[ELF_NVSRHALFREG];					\
> > > +	int i;								\
> > > +									\
> > > +	unsafe_copy_from_user(buf, __f,					\
> > > +				ELF_NVSRHALFREG * sizeof(double),	\
> > > +				label);					\
> > > +	for (i = 0; i < ELF_NVSRHALFREG ; i++)				\
> > > +		__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];	\
> > > +} while (0)
> > > +
> > > +
> > >  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> > >  #define unsafe_copy_ckfpr_to_user(to, task, label)	do {		\
> > >  	struct task_struct *__t = task;					\
> > > @@ -80,6 +107,10 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
> > >  	unsafe_copy_to_user(to, (task)->thread.fp_state.fpr,	\
> > >  			    ELF_NFPREG * sizeof(double), label)
> > > 
> > > +#define unsafe_copy_fpr_from_user(task, from, label)			\
> > > +	unsafe_copy_from_user((task)->thread.fp_state.fpr, from,	\
> > > +			    ELF_NFPREG * sizeof(double), label)
> > > +
> > >  static inline unsigned long
> > >  copy_fpr_to_user(void __user *to, struct task_struct *task)
> > >  {
> > > @@ -115,6 +146,8 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
> > >  #else
> > >  #define unsafe_copy_fpr_to_user(to, task, label) do { } while (0)
> > > 
> > > +#define unsafe_copy_fpr_from_user(task, from, label) do { } while (0)
> > > +
> > >  static inline unsigned long
> > >  copy_fpr_to_user(void __user *to, struct task_struct *task)
> > >  {
> > > --
> > > 2.26.1
> >
> > -
> > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
> > MK1 1PT, UK
> > Registration No: 1397386 (Wales)
> 
 

RE: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Christopher M. Riedl]

On Mon Feb 1, 2021 at 10:15 AM CST, David Laight wrote:
> From: Christopher M. Riedl
> > Sent: 01 February 2021 15:56
> > 
> > On Thu Jan 28, 2021 at 4:38 AM CST, David Laight wrote:
> > > From: Christopher M. Riedl
> > > > Sent: 28 January 2021 04:04
> > > >
> > > > Reuse the "safe" implementation from signal.c except for calling
> > > > unsafe_copy_from_user() to copy into a local buffer.
> > > >
> > > > Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> > > > ---
> > > >  arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
> > > >  1 file changed, 33 insertions(+)
> > > >
> > > > diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> > > > index 2559a681536e..c18402d625f1 100644
> > > > --- a/arch/powerpc/kernel/signal.h
> > > > +++ b/arch/powerpc/kernel/signal.h
> > > > @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
> > > >  				&buf[i], label);\
> > > >  } while (0)
> > > >
> > > > +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
> > > > +	struct task_struct *__t = task;					\
> > > > +	u64 __user *__f = (u64 __user *)from;				\
> > > > +	u64 buf[ELF_NFPREG];						\
> > >
> > > How big is that buffer?
> > > Isn't is likely to be reasonably large compared to a reasonable
> > > kernel stack frame.
> > > Especially since this isn't even a leaf function.
> > >
> > 
> > I think Christophe answered this - I don't really have an opinion either
> > way. What would be a 'reasonable' kernel stack frame for reference?
>
> Zero :-)
>

Hehe good point!

> > 
> > > > +	int i;								\
> > > > +									\
> > > > +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
> > > > +				label);					\
> > > > +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> > > > +		__t->thread.TS_FPR(i) = buf[i];				\
> > > > +	__t->thread.fp_state.fpscr = buf[i];				\
> > > > +} while (0)
>
> On further reflection, since you immediately loop through the buffer
> why not just use user_access_begin() and unsafe_get_user() in the loop.

Christophe had suggested this a few revisions ago as well. When I tried
this approach, the signal handling performance took a pretty big hit:
https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-October/219351.html

I included some numbers on v3 as well but decided to drop the approach
altogether for this one since it just didn't seem worth the hit.

>
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
> MK1 1PT, UK
> Registration No: 1397386 (Wales)

RE: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[David Laight]

From: Christopher M. Riedl
> Sent: 01 February 2021 16:55
...
> > > > > +	int i;								\
> > > > > +									\
> > > > > +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
> > > > > +				label);					\
> > > > > +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> > > > > +		__t->thread.TS_FPR(i) = buf[i];				\
> > > > > +	__t->thread.fp_state.fpscr = buf[i];				\
> > > > > +} while (0)
> >
> > On further reflection, since you immediately loop through the buffer
> > why not just use user_access_begin() and unsafe_get_user() in the loop.
> 
> Christophe had suggested this a few revisions ago as well. When I tried
> this approach, the signal handling performance took a pretty big hit:
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-October/219351.html
> 
> I included some numbers on v3 as well but decided to drop the approach
> altogether for this one since it just didn't seem worth the hit.

Was that using unsafe_get_user (which relies on user_access_begin()
having 'opened up' user accesses) or just get_user() that does
it for every access?

The former should be ok, the latter will be horrid.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

RE: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Christopher M. Riedl]

On Mon Feb 1, 2021 at 11:37 AM CST, David Laight wrote:
> From: Christopher M. Riedl
> > Sent: 01 February 2021 16:55
> ...
> > > > > > +	int i;								\
> > > > > > +									\
> > > > > > +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
> > > > > > +				label);					\
> > > > > > +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> > > > > > +		__t->thread.TS_FPR(i) = buf[i];				\
> > > > > > +	__t->thread.fp_state.fpscr = buf[i];				\
> > > > > > +} while (0)
> > >
> > > On further reflection, since you immediately loop through the buffer
> > > why not just use user_access_begin() and unsafe_get_user() in the loop.
> > 
> > Christophe had suggested this a few revisions ago as well. When I tried
> > this approach, the signal handling performance took a pretty big hit:
> > https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-October/219351.html
> > 
> > I included some numbers on v3 as well but decided to drop the approach
> > altogether for this one since it just didn't seem worth the hit.
>
> Was that using unsafe_get_user (which relies on user_access_begin()
> having 'opened up' user accesses) or just get_user() that does
> it for every access?
>
> The former should be ok, the latter will be horrid.

It was using unsafe_get_user() whereas unsafe_copy_from_user() will just
call the optimized __copy_tofrom_user() a single time - assuming that
user access is open.

>
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
> MK1 1PT, UK
> Registration No: 1397386 (Wales)

Re: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Christopher M. Riedl]

On Mon Feb 1, 2021 at 10:54 AM CST, Gabriel Paubert wrote:
> On Mon, Feb 01, 2021 at 09:55:44AM -0600, Christopher M. Riedl wrote:
> > On Thu Jan 28, 2021 at 4:38 AM CST, David Laight wrote:
> > > From: Christopher M. Riedl
> > > > Sent: 28 January 2021 04:04
> > > > 
> > > > Reuse the "safe" implementation from signal.c except for calling
> > > > unsafe_copy_from_user() to copy into a local buffer.
> > > > 
> > > > Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> > > > ---
> > > >  arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
> > > >  1 file changed, 33 insertions(+)
> > > > 
> > > > diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
> > > > index 2559a681536e..c18402d625f1 100644
> > > > --- a/arch/powerpc/kernel/signal.h
> > > > +++ b/arch/powerpc/kernel/signal.h
> > > > @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
> > > >  				&buf[i], label);\
> > > >  } while (0)
> > > > 
> > > > +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
> > > > +	struct task_struct *__t = task;					\
> > > > +	u64 __user *__f = (u64 __user *)from;				\
> > > > +	u64 buf[ELF_NFPREG];						\
> > >
> > > How big is that buffer?
> > > Isn't is likely to be reasonably large compared to a reasonable
> > > kernel stack frame.
> > > Especially since this isn't even a leaf function.
> > >
> > 
> > I think Christophe answered this - I don't really have an opinion either
> > way. What would be a 'reasonable' kernel stack frame for reference?
>
> See include/linux/poll.h, where the limit is of the order of 800 bytes
> and the number of entries in an on stack array is chosen at compile time
> (different between 32 and 64 bit for example).
>
> The values are used in do_sys_poll, which, with almost 1000 bytes of
> stack footprint, appears close to the top of "make checkstack". In
> addition do_sys_poll has to call the ->poll function of every file
> descriptor in its table, so it is not a tail function.
>
> This 264 bytes array looks reasonable, but please use 'make checkstack'
> to verify that the function's total stack usage stays within reason.

Neat, looks like total usage is a bit larger but still reasonable and
less than half of 800B:

0xc000000000017e900 __unsafe_restore_sigcontext.constprop.0 [vmlinux]:352

Thanks for the tip!

>
> Gabriel
>
> > 
> > > > +	int i;								\
> > > > +									\
> > > > +	unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double),	\
> > >
> > > That really ought to be sizeof(buf).
> > >
> > 
> > Agreed, I will fix this. Thanks!
> > 
> > > David
> > >
> > >
> > > > +				label);					\
> > > > +	for (i = 0; i < ELF_NFPREG - 1; i++)				\
> > > > +		__t->thread.TS_FPR(i) = buf[i];				\
> > > > +	__t->thread.fp_state.fpscr = buf[i];				\
> > > > +} while (0)
> > > > +
> > > > +#define unsafe_copy_vsx_from_user(task, from, label)	do {		\
> > > > +	struct task_struct *__t = task;					\
> > > > +	u64 __user *__f = (u64 __user *)from;				\
> > > > +	u64 buf[ELF_NVSRHALFREG];					\
> > > > +	int i;								\
> > > > +									\
> > > > +	unsafe_copy_from_user(buf, __f,					\
> > > > +				ELF_NVSRHALFREG * sizeof(double),	\
> > > > +				label);					\
> > > > +	for (i = 0; i < ELF_NVSRHALFREG ; i++)				\
> > > > +		__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];	\
> > > > +} while (0)
> > > > +
> > > > +
> > > >  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> > > >  #define unsafe_copy_ckfpr_to_user(to, task, label)	do {		\
> > > >  	struct task_struct *__t = task;					\
> > > > @@ -80,6 +107,10 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
> > > >  	unsafe_copy_to_user(to, (task)->thread.fp_state.fpr,	\
> > > >  			    ELF_NFPREG * sizeof(double), label)
> > > > 
> > > > +#define unsafe_copy_fpr_from_user(task, from, label)			\
> > > > +	unsafe_copy_from_user((task)->thread.fp_state.fpr, from,	\
> > > > +			    ELF_NFPREG * sizeof(double), label)
> > > > +
> > > >  static inline unsigned long
> > > >  copy_fpr_to_user(void __user *to, struct task_struct *task)
> > > >  {
> > > > @@ -115,6 +146,8 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
> > > >  #else
> > > >  #define unsafe_copy_fpr_to_user(to, task, label) do { } while (0)
> > > > 
> > > > +#define unsafe_copy_fpr_from_user(task, from, label) do { } while (0)
> > > > +
> > > >  static inline unsigned long
> > > >  copy_fpr_to_user(void __user *to, struct task_struct *task)
> > > >  {
> > > > --
> > > > 2.26.1
> > >
> > > -
> > > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes,
> > > MK1 1PT, UK
> > > Registration No: 1397386 (Wales)
> > 
>  

Re: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Michael Ellerman]

"Christopher M. Riedl" <cmr@codefail.de> writes:
> On Mon Feb 1, 2021 at 10:54 AM CST, Gabriel Paubert wrote:
>> On Mon, Feb 01, 2021 at 09:55:44AM -0600, Christopher M. Riedl wrote:
>> > On Thu Jan 28, 2021 at 4:38 AM CST, David Laight wrote:
>> > > From: Christopher M. Riedl
>> > > > Sent: 28 January 2021 04:04
>> > > > 
>> > > > Reuse the "safe" implementation from signal.c except for calling
>> > > > unsafe_copy_from_user() to copy into a local buffer.
>> > > > 
>> > > > Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
>> > > > ---
>> > > >  arch/powerpc/kernel/signal.h | 33 +++++++++++++++++++++++++++++++++
>> > > >  1 file changed, 33 insertions(+)
>> > > > 
>> > > > diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
>> > > > index 2559a681536e..c18402d625f1 100644
>> > > > --- a/arch/powerpc/kernel/signal.h
>> > > > +++ b/arch/powerpc/kernel/signal.h
>> > > > @@ -53,6 +53,33 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
>> > > >  				&buf[i], label);\
>> > > >  } while (0)
>> > > > 
>> > > > +#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
>> > > > +	struct task_struct *__t = task;					\
>> > > > +	u64 __user *__f = (u64 __user *)from;				\
>> > > > +	u64 buf[ELF_NFPREG];						\
>> > >
>> > > How big is that buffer?
>> > > Isn't is likely to be reasonably large compared to a reasonable
>> > > kernel stack frame.
>> > > Especially since this isn't even a leaf function.
>> > >
>> > 
>> > I think Christophe answered this - I don't really have an opinion either
>> > way. What would be a 'reasonable' kernel stack frame for reference?
>>
>> See include/linux/poll.h, where the limit is of the order of 800 bytes
>> and the number of entries in an on stack array is chosen at compile time
>> (different between 32 and 64 bit for example).
>>
>> The values are used in do_sys_poll, which, with almost 1000 bytes of
>> stack footprint, appears close to the top of "make checkstack". In
>> addition do_sys_poll has to call the ->poll function of every file
>> descriptor in its table, so it is not a tail function.
>>
>> This 264 bytes array looks reasonable, but please use 'make checkstack'
>> to verify that the function's total stack usage stays within reason.
>
> Neat, looks like total usage is a bit larger but still reasonable and
> less than half of 800B:
>
> 0xc000000000017e900 __unsafe_restore_sigcontext.constprop.0 [vmlinux]:352

We warn for frames larger than 2KB on 64-bit, see FRAME_WARN in
lib/Kconfig.debug.

So 264 bytes is entirely reasonable IMHO.

cheers