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Subject[PATCHv5 08/21] arm64: convert raw syscall invocation to C
Date
As a first step towards invoking syscalls with a pt_regs argument,
convert the raw syscall invocation logic to C. We end up with a bit more
register shuffling, but the unified invocation logic means we can unify
the tracing paths, too.

Previously, assembly had to open-code calls to ni_sys() when the system
call number was out-of-bounds for the relevant syscall table. This case
is now handled by invoke_syscall(), and the assembly no longer need to
handle this case explicitly. This allows the tracing paths to be
simplified and unified, as we no longer need the __ni_sys_trace path and
the __sys_trace_return label.

This only converts the invocation of the syscall. The rest of the
syscall triage and tracing is left in assembly for now, and will be
converted in subsequent patches.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
---
arch/arm64/kernel/Makefile | 3 ++-
arch/arm64/kernel/entry.S | 36 ++++++++++------------------------
arch/arm64/kernel/syscall.c | 47 +++++++++++++++++++++++++++++++++++++++++++++
arch/arm64/kernel/traps.c | 16 ---------------
4 files changed, 59 insertions(+), 43 deletions(-)
create mode 100644 arch/arm64/kernel/syscall.c

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 0025f8691046..4e24d2244bd1 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -18,7 +18,8 @@ arm64-obj-y := debug-monitors.o entry.o irq.o fpsimd.o \
hyp-stub.o psci.o cpu_ops.o insn.o \
return_address.o cpuinfo.o cpu_errata.o \
cpufeature.o alternative.o cacheinfo.o \
- smp.o smp_spin_table.o topology.o smccc-call.o
+ smp.o smp_spin_table.o topology.o smccc-call.o \
+ syscall.o

extra-$(CONFIG_EFI) := efi-entry.o

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 62f2876f9c63..c0392f78e392 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -903,7 +903,6 @@ ENDPROC(el0_error)
*/
ret_fast_syscall:
disable_daif
- str x0, [sp, #S_X0] // returned x0
ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing
and x2, x1, #_TIF_SYSCALL_WORK
cbnz x2, ret_fast_syscall_trace
@@ -976,15 +975,11 @@ el0_svc_naked: // compat entry point

tst x16, #_TIF_SYSCALL_WORK // check for syscall hooks
b.ne __sys_trace
- cmp wscno, wsc_nr // check upper syscall limit
- b.hs ni_sys
- mask_nospec64 xscno, xsc_nr, x19 // enforce bounds for syscall number
- ldr x16, [stbl, xscno, lsl #3] // address in the syscall table
- blr x16 // call sys_* routine
- b ret_fast_syscall
-ni_sys:
mov x0, sp
- bl do_ni_syscall
+ mov w1, wscno
+ mov w2, wsc_nr
+ mov x3, stbl
+ bl invoke_syscall
b ret_fast_syscall
ENDPROC(el0_svc)

@@ -1001,29 +996,18 @@ __sys_trace:
bl syscall_trace_enter
cmp w0, #NO_SYSCALL // skip the syscall?
b.eq __sys_trace_return_skipped
- mov wscno, w0 // syscall number (possibly new)
- mov x1, sp // pointer to regs
- cmp wscno, wsc_nr // check upper syscall limit
- b.hs __ni_sys_trace
- ldp x0, x1, [sp] // restore the syscall args
- ldp x2, x3, [sp, #S_X2]
- ldp x4, x5, [sp, #S_X4]
- ldp x6, x7, [sp, #S_X6]
- ldr x16, [stbl, xscno, lsl #3] // address in the syscall table
- blr x16 // call sys_* routine

-__sys_trace_return:
- str x0, [sp, #S_X0] // save returned x0
+ mov x0, sp
+ mov w1, wscno
+ mov w2, wsc_nr
+ mov x3, stbl
+ bl invoke_syscall
+
__sys_trace_return_skipped:
mov x0, sp
bl syscall_trace_exit
b ret_to_user

-__ni_sys_trace:
- mov x0, sp
- bl do_ni_syscall
- b __sys_trace_return
-
.popsection // .entry.text

#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
new file mode 100644
index 000000000000..93d36f22647e
--- /dev/null
+++ b/arch/arm64/kernel/syscall.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/errno.h>
+#include <linux/nospec.h>
+#include <linux/ptrace.h>
+#include <linux/syscalls.h>
+
+#include <asm/syscall.h>
+
+long compat_arm_syscall(struct pt_regs *regs);
+
+asmlinkage long do_ni_syscall(struct pt_regs *regs)
+{
+#ifdef CONFIG_COMPAT
+ long ret;
+ if (is_compat_task()) {
+ ret = compat_arm_syscall(regs);
+ if (ret != -ENOSYS)
+ return ret;
+ }
+#endif
+
+ return sys_ni_syscall();
+}
+
+static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
+{
+ return syscall_fn(regs->regs[0], regs->regs[1], regs->regs[2],
+ regs->regs[3], regs->regs[4], regs->regs[5]);
+}
+
+asmlinkage void invoke_syscall(struct pt_regs *regs, unsigned int scno,
+ unsigned int sc_nr,
+ const syscall_fn_t syscall_table[])
+{
+ long ret;
+
+ if (scno < sc_nr) {
+ syscall_fn_t syscall_fn;
+ syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
+ ret = __invoke_syscall(regs, syscall_fn);
+ } else {
+ ret = do_ni_syscall(regs);
+ }
+
+ regs->regs[0] = ret;
+}
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index c27292703bd1..039e9ff379cc 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -547,22 +547,6 @@ asmlinkage void __exception do_sysinstr(unsigned int esr, struct pt_regs *regs)
do_undefinstr(regs);
}

-long compat_arm_syscall(struct pt_regs *regs);
-
-asmlinkage long do_ni_syscall(struct pt_regs *regs)
-{
-#ifdef CONFIG_COMPAT
- long ret;
- if (is_compat_task()) {
- ret = compat_arm_syscall(regs);
- if (ret != -ENOSYS)
- return ret;
- }
-#endif
-
- return sys_ni_syscall();
-}
-
static const char *esr_class_str[] = {
[0 ... ESR_ELx_EC_MAX] = "UNRECOGNIZED EC",
[ESR_ELx_EC_UNKNOWN] = "Unknown/Uncategorized",
--
2.11.0
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