Commit 35d0e6fb authored by Dave Martin's avatar Dave Martin Committed by Catalin Marinas
Browse files

arm64: syscallno is secretly an int, make it official



The upper 32 bits of the syscallno field in thread_struct are
handled inconsistently, being sometimes zero extended and sometimes
sign-extended.  In fact, only the lower 32 bits seem to have any
real significance for the behaviour of the code: it's been OK to
handle the upper bits inconsistently because they don't matter.

Currently, the only place I can find where those bits are
significant is in calling trace_sys_enter(), which may be
unintentional: for example, if a compat tracer attempts to cancel a
syscall by passing -1 to (COMPAT_)PTRACE_SET_SYSCALL at the
syscall-enter-stop, it will be traced as syscall 4294967295
rather than -1 as might be expected (and as occurs for a native
tracer doing the same thing).  Elsewhere, reads of syscallno cast
it to an int or truncate it.

There's also a conspicuous amount of code and casting to bodge
around the fact that although semantically an int, syscallno is
stored as a u64.

Let's not pretend any more.

In order to preserve the stp x instruction that stores the syscall
number in entry.S, this patch special-cases the layout of struct
pt_regs for big endian so that the newly 32-bit syscallno field
maps onto the low bits of the stored value.  This is not beautiful,
but benchmarking of the getpid syscall on Juno suggests indicates a
minor slowdown if the stp is split into an stp x and stp w.
Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent aae4e7a8
......@@ -112,7 +112,7 @@ void tls_preserve_current_state(void);
static inline void start_thread_common(struct pt_regs *regs, unsigned long pc)
{
memset(regs, 0, sizeof(*regs));
regs->syscallno = ~0UL;
regs->syscallno = ~0;
regs->pc = pc;
}
......
......@@ -116,7 +116,14 @@ struct pt_regs {
};
};
u64 orig_x0;
u64 syscallno;
#ifdef __AARCH64EB__
u32 unused2;
s32 syscallno;
#else
s32 syscallno;
u32 unused2;
#endif
u64 orig_addr_limit;
u64 unused; // maintain 16 byte alignment
};
......
......@@ -142,8 +142,8 @@ alternative_else_nop_endif
* Set syscallno to -1 by default (overridden later if real syscall).
*/
.if \el == 0
mvn x21, xzr
str x21, [sp, #S_SYSCALLNO]
mvn w21, wzr
str w21, [sp, #S_SYSCALLNO]
.endif
/*
......@@ -290,8 +290,9 @@ alternative_else_nop_endif
*
* x7 is reserved for the system call number in 32-bit mode.
*/
sc_nr .req x25 // number of system calls
scno .req x26 // syscall number
wsc_nr .req w25 // number of system calls
wscno .req w26 // syscall number
xscno .req x26 // syscall number (zero-extended)
stbl .req x27 // syscall table pointer
tsk .req x28 // current thread_info
......@@ -577,8 +578,8 @@ el0_svc_compat:
* AArch32 syscall handling
*/
adrp stbl, compat_sys_call_table // load compat syscall table pointer
uxtw scno, w7 // syscall number in w7 (r7)
mov sc_nr, #__NR_compat_syscalls
mov wscno, w7 // syscall number in w7 (r7)
mov wsc_nr, #__NR_compat_syscalls
b el0_svc_naked
.align 6
......@@ -798,19 +799,19 @@ ENDPROC(ret_from_fork)
.align 6
el0_svc:
adrp stbl, sys_call_table // load syscall table pointer
uxtw scno, w8 // syscall number in w8
mov sc_nr, #__NR_syscalls
mov wscno, w8 // syscall number in w8
mov wsc_nr, #__NR_syscalls
el0_svc_naked: // compat entry point
stp x0, scno, [sp, #S_ORIG_X0] // save the original x0 and syscall number
stp x0, xscno, [sp, #S_ORIG_X0] // save the original x0 and syscall number
enable_dbg_and_irq
ct_user_exit 1
ldr x16, [tsk, #TSK_TI_FLAGS] // check for syscall hooks
tst x16, #_TIF_SYSCALL_WORK
b.ne __sys_trace
cmp scno, sc_nr // check upper syscall limit
cmp wscno, wsc_nr // check upper syscall limit
b.hs ni_sys
ldr x16, [stbl, scno, lsl #3] // address in the syscall table
ldr x16, [stbl, xscno, lsl #3] // address in the syscall table
blr x16 // call sys_* routine
b ret_fast_syscall
ni_sys:
......@@ -824,24 +825,23 @@ ENDPROC(el0_svc)
* switches, and waiting for our parent to respond.
*/
__sys_trace:
mov w0, #-1 // set default errno for
cmp scno, x0 // user-issued syscall(-1)
cmp wscno, #-1 // user-issued syscall(-1)?
b.ne 1f
mov x0, #-ENOSYS
mov x0, #-ENOSYS // set default errno if so
str x0, [sp, #S_X0]
1: mov x0, sp
bl syscall_trace_enter
cmp w0, #-1 // skip the syscall?
b.eq __sys_trace_return_skipped
uxtw scno, w0 // syscall number (possibly new)
mov wscno, w0 // syscall number (possibly new)
mov x1, sp // pointer to regs
cmp scno, sc_nr // check upper syscall limit
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, scno, lsl #3] // address in the syscall table
ldr x16, [stbl, xscno, lsl #3] // address in the syscall table
blr x16 // call sys_* routine
__sys_trace_return:
......
......@@ -1363,7 +1363,7 @@ static void tracehook_report_syscall(struct pt_regs *regs,
if (dir == PTRACE_SYSCALL_EXIT)
tracehook_report_syscall_exit(regs, 0);
else if (tracehook_report_syscall_entry(regs))
regs->syscallno = ~0UL;
regs->syscallno = ~0;
regs->regs[regno] = saved_reg;
}
......
......@@ -387,7 +387,7 @@ static int restore_sigframe(struct pt_regs *regs,
/*
* Avoid sys_rt_sigreturn() restarting.
*/
regs->syscallno = ~0UL;
regs->syscallno = ~0;
err |= !valid_user_regs(&regs->user_regs, current);
if (err == 0)
......@@ -673,7 +673,7 @@ static void do_signal(struct pt_regs *regs)
{
unsigned long continue_addr = 0, restart_addr = 0;
int retval = 0;
int syscall = (int)regs->syscallno;
int syscall = regs->syscallno;
struct ksignal ksig;
/*
......@@ -687,7 +687,7 @@ static void do_signal(struct pt_regs *regs)
/*
* Avoid additional syscall restarting via ret_to_user.
*/
regs->syscallno = ~0UL;
regs->syscallno = ~0;
/*
* Prepare for system call restart. We do this here so that a
......
......@@ -354,7 +354,7 @@ static int compat_restore_sigframe(struct pt_regs *regs,
/*
* Avoid compat_sys_sigreturn() restarting.
*/
regs->syscallno = ~0UL;
regs->syscallno = ~0;
err |= !valid_user_regs(&regs->user_regs, current);
......
......@@ -593,7 +593,7 @@ asmlinkage long do_ni_syscall(struct pt_regs *regs)
if (show_unhandled_signals_ratelimited()) {
pr_info("%s[%d]: syscall %d\n", current->comm,
task_pid_nr(current), (int)regs->syscallno);
task_pid_nr(current), regs->syscallno);
dump_instr("", regs);
if (user_mode(regs))
__show_regs(regs);
......
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