[RFC WIP PATCH] powerpc/32: system call implement entry/exit logic in C

From: Christophe Leroy
Date: Tue Mar 31 2020 - 11:23:01 EST

That's first try to port PPC64 syscall entry/exit logic in C to PPC32.
I've do the minimum to get it work. I have not reworked calls
to sys_fork() and friends for instance.

For the time being, it seems to work more or less but:
- ping reports EINVAL on recvfrom
- strace shows NULL instead of strings in call like open() for instance.
- the performance is definitively bad

On an 8xx, null_syscall test is about 30% slower after this patch:
- Without the patch: 284 cycles
- With the patch: 371 cycles

@nick and others, any suggestion to fix and improve ?

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/include/asm/book3s/32/kup.h | 21 ++
.../powerpc/include/asm/book3s/64/kup-radix.h | 12 +-
arch/powerpc/include/asm/hw_irq.h | 15 +
arch/powerpc/include/asm/kup.h | 2 +
arch/powerpc/include/asm/nohash/32/kup-8xx.h | 13 +
arch/powerpc/kernel/Makefile | 5 +-
arch/powerpc/kernel/entry_32.S | 259 ++----------------
arch/powerpc/kernel/head_32.h | 3 +-
.../kernel/{syscall_64.c => syscall.c} | 25 +-
9 files changed, 102 insertions(+), 253 deletions(-)
rename arch/powerpc/kernel/{syscall_64.c => syscall.c} (97%)

diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
index 3c0ba22dc360..c85bc5b56366 100644
--- a/arch/powerpc/include/asm/book3s/32/kup.h
+++ b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -102,6 +102,27 @@ static inline void kuap_update_sr(u32 sr, u32 addr, u32 end)
isync(); /* Context sync required after mtsrin() */
}

+static inline void kuap_restore(struct pt_regs *regs)
+{
+ u32 kuap = current->thread.kuap;
+ u32 addr = kuap & 0xf0000000;
+ u32 end = kuap << 28;
+
+ if (unlikely(!kuap))
+ return;
+
+ current->thread.kuap = 0;
+ kuap_update_sr(mfsrin(addr) & ~SR_KS, addr, end); /* Clear Ks */
+}
+
+static inline void kuap_check(void)
+{
+ if (!IS_ENABLED(CONFIG_PPC_KUAP_DEBUG))
+ return;
+
+ WARN_ON_ONCE(current->thread.kuap != 0);
+}
+
static __always_inline void allow_user_access(void __user *to, const void __user *from,
u32 size, unsigned long dir)
{
diff --git a/arch/powerpc/include/asm/book3s/64/kup-radix.h b/arch/powerpc/include/asm/book3s/64/kup-radix.h
index 3bcef989a35d..1f2716a0dcd8 100644
--- a/arch/powerpc/include/asm/book3s/64/kup-radix.h
+++ b/arch/powerpc/include/asm/book3s/64/kup-radix.h
@@ -60,13 +60,13 @@
#include <asm/mmu.h>
#include <asm/ptrace.h>

-static inline void kuap_restore_amr(struct pt_regs *regs)
+static inline void kuap_restore(struct pt_regs *regs)
{
if (mmu_has_feature(MMU_FTR_RADIX_KUAP))
mtspr(SPRN_AMR, regs->kuap);
}

-static inline void kuap_check_amr(void)
+static inline void kuap_check(void)
{
if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG) && mmu_has_feature(MMU_FTR_RADIX_KUAP))
WARN_ON_ONCE(mfspr(SPRN_AMR) != AMR_KUAP_BLOCKED);
@@ -141,14 +141,6 @@ bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
(regs->kuap & (is_write ? AMR_KUAP_BLOCK_WRITE : AMR_KUAP_BLOCK_READ)),
"Bug: %s fault blocked by AMR!", is_write ? "Write" : "Read");
}
-#else /* CONFIG_PPC_KUAP */
-static inline void kuap_restore_amr(struct pt_regs *regs)
-{
-}
-
-static inline void kuap_check_amr(void)
-{
-}
#endif /* CONFIG_PPC_KUAP */

#endif /* __ASSEMBLY__ */
diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index e0e71777961f..6ccf07de6665 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h
@@ -321,6 +321,16 @@ static inline void arch_local_irq_disable(void)
mtmsr(mfmsr() & ~MSR_EE);
}

+static inline void arch_local_recovery_disable(void)
+{
+ if (IS_ENABLED(CONFIG_BOOKE))
+ wrtee(0);
+ else if (IS_ENABLED(CONFIG_PPC_8xx))
+ wrtspr(SPRN_NRI);
+ else
+ mtmsr(mfmsr() & ~(MSR_EE | MSR_RI));
+}
+
static inline void arch_local_irq_enable(void)
{
if (IS_ENABLED(CONFIG_BOOKE))
@@ -343,6 +353,11 @@ static inline bool arch_irqs_disabled(void)

#define hard_irq_disable() arch_local_irq_disable()

+#define __hard_irq_enable() arch_local_irq_enable()
+#define __hard_irq_disable() arch_local_irq_disable()
+#define __hard_EE_RI_disable() arch_local_recovery_disable()
+#define __hard_RI_enable() arch_local_irq_disable()
+
static inline bool arch_irq_disabled_regs(struct pt_regs *regs)
{
return !(regs->msr & MSR_EE);
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 92bcd1a26d73..1100c13b6d9e 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -62,6 +62,8 @@ bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{
return false;
}
+static inline void kuap_restore(struct pt_regs *regs) { }
+static inline void kuap_check(void) { }
#endif /* CONFIG_PPC_KUAP */

static inline void allow_read_from_user(const void __user *from, unsigned long size)
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
index 85ed2390fb99..1918d2e55da3 100644
--- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
@@ -34,6 +34,19 @@

#include <asm/reg.h>

+static inline void kuap_restore(struct pt_regs *regs)
+{
+ mtspr(SPRN_MD_AP, regs->kuap);
+}
+
+static inline void kuap_check(void)
+{
+ if (!IS_ENABLED(CONFIG_PPC_KUAP_DEBUG))
+ return;
+
+ WARN_ON_ONCE((mfspr(SPRN_MD_AP) & 0xffff0000) != (MD_APG_KUAP & 0xffff0000));
+}
+
static inline void allow_user_access(void __user *to, const void __user *from,
unsigned long size, unsigned long dir)
{
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 570660efbb3d..e4be425b7718 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -45,11 +45,10 @@ obj-y := cputable.o syscalls.o \
signal.o sysfs.o cacheinfo.o time.o \
prom.o traps.o setup-common.o \
udbg.o misc.o io.o misc_$(BITS).o \
- of_platform.o prom_parse.o
+ of_platform.o prom_parse.o syscall.o
obj-y += ptrace/
obj-$(CONFIG_PPC64) += setup_64.o sys_ppc32.o signal_64.o \
- paca.o nvram_64.o firmware.o note.o \
- syscall_64.o
+ paca.o nvram_64.o firmware.o note.o
obj-$(CONFIG_VDSO32) += vdso32/
obj-$(CONFIG_PPC_WATCHDOG) += watchdog.o
obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index a6371fb8f761..103f5158bc44 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -315,162 +315,37 @@ stack_ovf:
RFI
#endif

-#ifdef CONFIG_TRACE_IRQFLAGS
-trace_syscall_entry_irq_off:
- /*
- * Syscall shouldn't happen while interrupts are disabled,
- * so let's do a warning here.
- */
-0: trap
- EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
- bl trace_hardirqs_on
-
- /* Now enable for real */
- LOAD_REG_IMMEDIATE(r10, MSR_KERNEL | MSR_EE)
- mtmsr r10
-
- REST_GPR(0, r1)
- REST_4GPRS(3, r1)
- REST_2GPRS(7, r1)
- b DoSyscall
-#endif /* CONFIG_TRACE_IRQFLAGS */
-
.globl transfer_to_syscall
transfer_to_syscall:
-#ifdef CONFIG_TRACE_IRQFLAGS
- andi. r12,r9,MSR_EE
- beq- trace_syscall_entry_irq_off
-#endif /* CONFIG_TRACE_IRQFLAGS */
-
-/*
- * Handle a system call.
- */
- .stabs "arch/powerpc/kernel/",N_SO,0,0,0f
- .stabs "entry_32.S",N_SO,0,0,0f
-0:
-
-_GLOBAL(DoSyscall)
- stw r3,ORIG_GPR3(r1)
- li r12,0
- stw r12,RESULT(r1)
-#ifdef CONFIG_TRACE_IRQFLAGS
- /* Make sure interrupts are enabled */
- mfmsr r11
- andi. r12,r11,MSR_EE
- /* We came in with interrupts disabled, we WARN and mark them enabled
- * for lockdep now */
-0: tweqi r12, 0
- EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
-#endif /* CONFIG_TRACE_IRQFLAGS */
- lwz r11,TI_FLAGS(r2)
- andi. r11,r11,_TIF_SYSCALL_DOTRACE
- bne- syscall_dotrace
-syscall_dotrace_cont:
- cmplwi 0,r0,NR_syscalls
- lis r10,sys_call_table@h
- ori r10,r10,sys_call_table@l
- slwi r0,r0,2
- bge- 66f
-
- barrier_nospec_asm
- /*
- * Prevent the load of the handler below (based on the user-passed
- * system call number) being speculatively executed until the test
- * against NR_syscalls and branch to .66f above has
- * committed.
- */
-
- lwzx r10,r10,r0 /* Fetch system call handler [ptr] */
- mtlr r10
- addi r9,r1,STACK_FRAME_OVERHEAD
- PPC440EP_ERR42
- blrl /* Call handler */
- .globl ret_from_syscall
+ mr r9, r0
+ addi r10, r1, STACK_FRAME_OVERHEAD
+ bl system_call_exception
ret_from_syscall:
-#ifdef CONFIG_DEBUG_RSEQ
- /* Check whether the syscall is issued inside a restartable sequence */
- stw r3,GPR3(r1)
- addi r3,r1,STACK_FRAME_OVERHEAD
- bl rseq_syscall
- lwz r3,GPR3(r1)
-#endif
- mr r6,r3
- /* disable interrupts so current_thread_info()->flags can't change */
- LOAD_REG_IMMEDIATE(r10,MSR_KERNEL) /* doesn't include MSR_EE */
- /* Note: We don't bother telling lockdep about it */
- SYNC
- mtmsr r10
- lwz r9,TI_FLAGS(r2)
- li r8,-MAX_ERRNO
- andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
- bne- syscall_exit_work
- cmplw 0,r3,r8
- blt+ syscall_exit_cont
- lwz r11,_CCR(r1) /* Load CR */
- neg r3,r3
- oris r11,r11,0x1000 /* Set SO bit in CR */
- stw r11,_CCR(r1)
-syscall_exit_cont:
- lwz r8,_MSR(r1)
-#ifdef CONFIG_TRACE_IRQFLAGS
- /* If we are going to return from the syscall with interrupts
- * off, we trace that here. It shouldn't normally happen.
- */
- andi. r10,r8,MSR_EE
- bne+ 1f
- stw r3,GPR3(r1)
- bl trace_hardirqs_off
- lwz r3,GPR3(r1)
-1:
-#endif /* CONFIG_TRACE_IRQFLAGS */
-#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
- /* If the process has its own DBCR0 value, load it up. The internal
- debug mode bit tells us that dbcr0 should be loaded. */
- lwz r0,THREAD+THREAD_DBCR0(r2)
- andis. r10,r0,DBCR0_IDM@h
- bnel- load_dbcr0
-#endif
-#ifdef CONFIG_44x
-BEGIN_MMU_FTR_SECTION
- lis r4,icache_44x_need_flush@ha
- lwz r5,icache_44x_need_flush@l(r4)
- cmplwi cr0,r5,0
- bne- 2f
-1:
-END_MMU_FTR_SECTION_IFCLR(MMU_FTR_TYPE_47x)
-#endif /* CONFIG_44x */
-BEGIN_FTR_SECTION
- lwarx r7,0,r1
-END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
- stwcx. r0,0,r1 /* to clear the reservation */
- ACCOUNT_CPU_USER_EXIT(r2, r5, r7)
-#ifdef CONFIG_PPC_BOOK3S_32
- kuep_unlock r5, r7
-#endif
- kuap_check r2, r4
- lwz r4,_LINK(r1)
- lwz r5,_CCR(r1)
- mtlr r4
- mtcr r5
- lwz r7,_NIP(r1)
- lwz r2,GPR2(r1)
- lwz r1,GPR1(r1)
-#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
- mtspr SPRN_NRI, r0
-#endif
- mtspr SPRN_SRR0,r7
- mtspr SPRN_SRR1,r8
- SYNC
- RFI
-#ifdef CONFIG_44x
-2: li r7,0
- iccci r0,r0
- stw r7,icache_44x_need_flush@l(r4)
+ addi r4, r1, STACK_FRAME_OVERHEAD
+ bl syscall_exit_prepare
+ lwz r2, _CCR(r1)
+ lwz r4, _NIP(r1)
+ lwz r5, _MSR(r1)
+ lwz r6, _LINK(r1)
+ mtspr SPRN_SRR0, r4
+ mtspr SPRN_SRR1, r5
+ mtlr r6
+ cmpwi r3, 0
+ bne 2f
+1: mtcr r2
+ REST_GPR(2, r1)
+ REST_GPR(3, r1)
+ REST_GPR(1, r1)
+ rfi
+2: lwz r3, _CTR(r1)
+ lwz r4, _XER(r1)
+ REST_NVGPRS(r1)
+ mtctr r3
+ mtspr SPRN_XER, r4
+ REST_GPR(0, r1)
+ REST_8GPRS(4, r1)
+ REST_GPR(12, r1)
b 1b
-#endif /* CONFIG_44x */
-
-66: li r3,-ENOSYS
- b ret_from_syscall

.globl ret_from_fork
ret_from_fork:
@@ -490,86 +365,6 @@ ret_from_kernel_thread:
li r3,0
b ret_from_syscall

-/* Traced system call support */
-syscall_dotrace:
- SAVE_NVGPRS(r1)
- li r0,0xc00
- stw r0,_TRAP(r1)
- addi r3,r1,STACK_FRAME_OVERHEAD
- bl do_syscall_trace_enter
- /*
- * Restore argument registers possibly just changed.
- * We use the return value of do_syscall_trace_enter
- * for call number to look up in the table (r0).
- */
- mr r0,r3
- lwz r3,GPR3(r1)
- lwz r4,GPR4(r1)
- lwz r5,GPR5(r1)
- lwz r6,GPR6(r1)
- lwz r7,GPR7(r1)
- lwz r8,GPR8(r1)
- REST_NVGPRS(r1)
-
- cmplwi r0,NR_syscalls
- /* Return code is already in r3 thanks to do_syscall_trace_enter() */
- bge- ret_from_syscall
- b syscall_dotrace_cont
-
-syscall_exit_work:
- andi. r0,r9,_TIF_RESTOREALL
- beq+ 0f
- REST_NVGPRS(r1)
- b 2f
-0: cmplw 0,r3,r8
- blt+ 1f
- andi. r0,r9,_TIF_NOERROR
- bne- 1f
- lwz r11,_CCR(r1) /* Load CR */
- neg r3,r3
- oris r11,r11,0x1000 /* Set SO bit in CR */
- stw r11,_CCR(r1)
-
-1: stw r6,RESULT(r1) /* Save result */
- stw r3,GPR3(r1) /* Update return value */
-2: andi. r0,r9,(_TIF_PERSYSCALL_MASK)
- beq 4f
-
- /* Clear per-syscall TIF flags if any are set. */
-
- li r11,_TIF_PERSYSCALL_MASK
- addi r12,r2,TI_FLAGS
-3: lwarx r8,0,r12
- andc r8,r8,r11
-#ifdef CONFIG_IBM405_ERR77
- dcbt 0,r12
-#endif
- stwcx. r8,0,r12
- bne- 3b
-
-4: /* Anything which requires enabling interrupts? */
- andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP)
- beq ret_from_except
-
- /* Re-enable interrupts. There is no need to trace that with
- * lockdep as we are supposed to have IRQs on at this point
- */
- ori r10,r10,MSR_EE
- SYNC
- mtmsr r10
-
- /* Save NVGPRS if they're not saved already */
- lwz r4,_TRAP(r1)
- andi. r4,r4,1
- beq 5f
- SAVE_NVGPRS(r1)
- li r4,0xc00
- stw r4,_TRAP(r1)
-5:
- addi r3,r1,STACK_FRAME_OVERHEAD
- bl do_syscall_trace_leave
- b ret_from_except_full
-
/*
* System call was called from kernel. We get here with SRR1 in r9.
* Mark the exception as recoverable once we have retrieved SRR0,
diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index 9abec6cd099c..97691931a306 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -174,12 +174,13 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
stw r2,GPR2(r11)
addi r10,r10,STACK_FRAME_REGS_MARKER@l
stw r9,_MSR(r11)
- li r2, \trapno + 1
+ li r2, \trapno
stw r10,8(r11)
stw r2,_TRAP(r11)
SAVE_GPR(0, r11)
SAVE_4GPRS(3, r11)
SAVE_2GPRS(7, r11)
+ SAVE_NVGPRS(r11)
addi r11,r1,STACK_FRAME_OVERHEAD
addi r2,r12,-THREAD
stw r11,PT_REGS(r12)
diff --git a/arch/powerpc/kernel/syscall_64.c b/arch/powerpc/kernel/syscall.c
similarity index 97%
rename from arch/powerpc/kernel/syscall_64.c
rename to arch/powerpc/kernel/syscall.c
index cf06eb443a80..a07702a85f81 100644
--- a/arch/powerpc/kernel/syscall_64.c
+++ b/arch/powerpc/kernel/syscall.c
@@ -1,8 +1,9 @@
// SPDX-License-Identifier: GPL-2.0-or-later

#include <linux/err.h>
+#include <linux/compat.h>
+
#include <asm/asm-prototypes.h>
-#include <asm/book3s/64/kup-radix.h>
#include <asm/cputime.h>
#include <asm/hw_irq.h>
#include <asm/kprobes.h>
@@ -25,16 +26,20 @@ notrace long system_call_exception(long r3, long r4, long r5,
unsigned long ti_flags;
syscall_fn f;

+#ifdef CONFIG_PPC64
if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
BUG_ON(irq_soft_mask_return() != IRQS_ALL_DISABLED);
+#endif

trace_hardirqs_off(); /* finish reconciling */

- if (IS_ENABLED(CONFIG_PPC_BOOK3S))
+ if (!IS_ENABLED(CONFIG_PPC_BOOK3E))
BUG_ON(!(regs->msr & MSR_RI));
BUG_ON(!(regs->msr & MSR_PR));
BUG_ON(!FULL_REGS(regs));
+#ifdef CONFIG_PPC64
BUG_ON(regs->softe != IRQS_ENABLED);
+#endif

account_cpu_user_entry();

@@ -48,7 +53,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
}
#endif

- kuap_check_amr();
+ kuap_check();

/*
* This is not required for the syscall exit path, but makes the
@@ -56,7 +61,9 @@ notrace long system_call_exception(long r3, long r4, long r5,
* frame, or if the unwinder was taught the first stack frame always
* returns to user with IRQS_ENABLED, this store could be avoided!
*/
+#ifdef CONFIG_PPC64
regs->softe = IRQS_ENABLED;
+#endif

local_irq_enable();

@@ -86,7 +93,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
/* May be faster to do array_index_nospec? */
barrier_nospec();

- if (unlikely(ti_flags & _TIF_32BIT)) {
+ if (is_compat_task()) {
f = (void *)compat_sys_call_table[r0];

r3 &= 0x00000000ffffffffULL;
@@ -148,7 +155,9 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
ret |= _TIF_RESTOREALL;
}

+#ifdef CONFIG_PPC64
again:
+#endif
local_irq_disable();
ti_flags = READ_ONCE(*ti_flagsp);
while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
@@ -191,6 +200,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,

/* This pattern matches prep_irq_for_idle */
__hard_EE_RI_disable();
+#ifdef CONFIG_PPC64
if (unlikely(lazy_irq_pending())) {
__hard_RI_enable();
trace_hardirqs_off();
@@ -201,12 +211,13 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
}
local_paca->irq_happened = 0;
irq_soft_mask_set(IRQS_ENABLED);
+#endif

#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
local_paca->tm_scratch = regs->msr;
#endif

- kuap_check_amr();
+ kuap_check();

account_cpu_user_exit();

@@ -294,7 +305,7 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned
local_paca->tm_scratch = regs->msr;
#endif

- kuap_check_amr();
+ kuap_check();

account_cpu_user_exit();

@@ -372,7 +383,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsign
* We don't need to restore AMR on the way back to userspace for KUAP.
* The value of AMR only matters while we're in the kernel.
*/
- kuap_restore_amr(regs);
+ kuap_restore(regs);

return ret;
}
--
2.25.0