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Mark Rutland authored
We use cpus_have_const_cap() to check for ARM64_WORKAROUND_1542419 but this is not necessary and cpus_have_final_cap() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. The ARM64_WORKAROUND_1542419 cpucap is detected and patched before any userspace code can run, and the both __do_compat_cache_op() and ctr_read_handler() are only reachable from exceptions taken from userspace. Thus it is not necessary for either to use cpus_have_const_cap(), and cpus_have_final_cap() is equivalent. This patch replaces the use of cpus_have_const_cap() with cpus_have_final_cap(), which will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. Using cpus_have_final_cap() clearly documents that we do not expect this code to run before cpucaps are finalized, and will make it easier to spot issues if code is changed in future to allow these functions to be reached earlier. Signed-off-by:
Mark Rutland <mark.rutland@arm.com> Cc: Suzuki K Poulose <suzuki.poulose@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by:
Catalin Marinas <catalin.marinas@arm.com>
d1e40f82
sys_compat.c 2.95 KiB
// SPDX-License-Identifier: GPL-2.0-only
/*
* Based on arch/arm/kernel/sys_arm.c
*
* Copyright (C) People who wrote linux/arch/i386/kernel/sys_i386.c
* Copyright (C) 1995, 1996 Russell King.
* Copyright (C) 2012 ARM Ltd.
*/
#include <linux/compat.h>
#include <linux/cpufeature.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/system_misc.h>
#include <asm/tlbflush.h>
#include <asm/unistd.h>
static long
__do_compat_cache_op(unsigned long start, unsigned long end)
{
long ret;
do {
unsigned long chunk = min(PAGE_SIZE, end - start);
if (fatal_signal_pending(current))
return 0;
if (cpus_have_final_cap(ARM64_WORKAROUND_1542419)) {
/*
* The workaround requires an inner-shareable tlbi.
* We pick the reserved-ASID to minimise the impact.
*/
__tlbi(aside1is, __TLBI_VADDR(0, 0));
dsb(ish);
}
ret = caches_clean_inval_user_pou(start, start + chunk);
if (ret)
return ret;
cond_resched();
start += chunk;
} while (start < end);
return 0;
}
static inline long
do_compat_cache_op(unsigned long start, unsigned long end, int flags)
{
if (end < start || flags)
return -EINVAL;
if (!access_ok((const void __user *)start, end - start))
return -EFAULT;
return __do_compat_cache_op(start, end);
}
/*
* Handle all unrecognised system calls.
*/
long compat_arm_syscall(struct pt_regs *regs, int scno)
{
unsigned long addr;
switch (scno) {
/*
* Flush a region from virtual address 'r0' to virtual address 'r1'
* _exclusive_. There is no alignment requirement on either address;
* user space does not need to know the hardware cache layout.
*
* r2 contains flags. It should ALWAYS be passed as ZERO until it
* is defined to be something else. For now we ignore it, but may
* the fires of hell burn in your belly if you break this rule. ;)
*
* (at a later date, we may want to allow this call to not flush
* various aspects of the cache. Passing '0' will guarantee that
* everything necessary gets flushed to maintain consistency in
* the specified region).
*/
case __ARM_NR_compat_cacheflush:
return do_compat_cache_op(regs->regs[0], regs->regs[1], regs->regs[2]);
case __ARM_NR_compat_set_tls:
current->thread.uw.tp_value = regs->regs[0];
/*
* Protect against register corruption from context switch.
* See comment in tls_thread_flush.
*/
barrier();
write_sysreg(regs->regs[0], tpidrro_el0);
return 0;
default:
/*
* Calls 0xf0xxx..0xf07ff are defined to return -ENOSYS
* if not implemented, rather than raising SIGILL. This
* way the calling program can gracefully determine whether
* a feature is supported.
*/
if (scno < __ARM_NR_COMPAT_END)
return -ENOSYS;
break;
}
addr = instruction_pointer(regs) - (compat_thumb_mode(regs) ? 2 : 4);
arm64_notify_die("Oops - bad compat syscall(2)", regs,
SIGILL, ILL_ILLTRP, addr, 0);
return 0;
}