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arm64: traps: fix userspace cache maintenance emulation on a tagged pointer 

When we emulate userspace cache maintenance in the kernel, we can
currently send the task a SIGSEGV even though the maintenance was done
on a valid address. This happens if the address has a non-zero address
tag, and happens to not be mapped in.

When we get the address from a user register, we don't currently remove
the address tag before performing cache maintenance on it. If the
maintenance faults, we end up in either __do_page_fault, where find_vma
can't find the VMA if the address has a tag, or in do_translation_fault,
where the tagged address will appear to be above TASK_SIZE. In both
cases, the address is not mapped in, and the task is sent a SIGSEGV.

This patch removes the tag from the address before using it. With this
patch, the fault is handled correctly, the address gets mapped in, and
the cache maintenance succeeds.

As a second bug, if cache maintenance (correctly) fails on an invalid
tagged address, the address gets passed into arm64_notify_segfault,
where find_vma fails to find the VMA due to the tag, and the wrong
si_code may be sent as part of the siginfo_t of the segfault. With this
patch, the correct si_code is sent.

Fixes: 7dd01aef05 ("arm64: trap userspace "dc cvau" cache operation on errata-affected core")
Cc: <stable@vger.kernel.org> # 4.8.x-
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Kristina Martsenko 2017-05-03 16:37:45 +01:00 committed by Catalin Marinas
parent 92f66f84d9
commit 81cddd65b5
1 changed files with 2 additions and 2 deletions
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4
arch/arm64/kernel/traps.c
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@ -443,7 +443,7 @@ int cpu_enable_cache_maint_trap(void *__unused)
}
#define __user_cache_maint(insn, address, res) \
if (untagged_addr(address) >= user_addr_max()) { \
if (address >= user_addr_max()) { \
res = -EFAULT; \
} else { \
uaccess_ttbr0_enable(); \
@ -469,7 +469,7 @@ static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
int crm = (esr & ESR_ELx_SYS64_ISS_CRM_MASK) >> ESR_ELx_SYS64_ISS_CRM_SHIFT;
int ret = 0;
address = pt_regs_read_reg(regs, rt);
address = untagged_addr(pt_regs_read_reg(regs, rt));
switch (crm) {
case ESR_ELx_SYS64_ISS_CRM_DC_CVAU: /* DC CVAU, gets promoted */