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author | Dave Martin <Dave.Martin@arm.com> | 2017-08-01 15:35:53 +0100 |
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committer | Catalin Marinas <catalin.marinas@arm.com> | 2017-08-07 09:58:33 +0100 |
commit | 35d0e6fb4d219d64ab3b7cffef7a11a0662140f5 (patch) | |
tree | ce5ac008ec803ea479d715b84515c59c6e68ef20 /arch/arm64/kernel/entry.S | |
parent | aae4e7a8bc44722fe70d58920a36916b1043195e (diff) | |
download | linux-stable-35d0e6fb4d219d64ab3b7cffef7a11a0662140f5.tar.gz linux-stable-35d0e6fb4d219d64ab3b7cffef7a11a0662140f5.tar.bz2 linux-stable-35d0e6fb4d219d64ab3b7cffef7a11a0662140f5.zip |
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: Dave Martin <Dave.Martin@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64/kernel/entry.S')
-rw-r--r-- | arch/arm64/kernel/entry.S | 34 |
1 files changed, 17 insertions, 17 deletions
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index b738880350f9..3bf0bd7a2f29 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -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: |