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arm64: kernel: Add support for User Access Override

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'User Access Override' is a new ARMv8.2 feature which allows the
unprivileged load and store instructions to be overridden to behave in
the normal way.

This patch converts {get,put}_user() and friends to use ldtr*/sttr*
instructions - so that they can only access EL0 memory, then enables
UAO when fs==KERNEL_DS so that these functions can access kernel memory.

This allows user space's read/write permissions to be checked against the
page tables, instead of testing addr<USER_DS, then using the kernel's
read/write permissions.

Signed-off-by: James Morse <james.morse@arm.com>
[catalin.marinas@arm.com: move uao_thread_switch() above dsb()]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
James Morse
2016-02-05 14:58:48 +00:00
committed by Catalin Marinas
parent 406e308770
commit 57f4959bad
15 changed files with 213 additions and 39 deletions
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31
arch/arm64/mm/fault.c
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@@ -192,6 +192,14 @@ out:
return fault;
}
static inline int permission_fault(unsigned int esr)
{
unsigned int ec = (esr & ESR_ELx_EC_MASK) >> ESR_ELx_EC_SHIFT;
unsigned int fsc_type = esr & ESR_ELx_FSC_TYPE;
return (ec == ESR_ELx_EC_DABT_CUR && fsc_type == ESR_ELx_FSC_PERM);
}
static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
struct pt_regs *regs)
{
@@ -225,12 +233,10 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
mm_flags |= FAULT_FLAG_WRITE;
}
/*
* PAN bit set implies the fault happened in kernel space, but not
* in the arch's user access functions.
*/
if (IS_ENABLED(CONFIG_ARM64_PAN) && (regs->pstate & PSR_PAN_BIT))
goto no_context;
if (permission_fault(esr) && (addr < USER_DS)) {
if (!search_exception_tables(regs->pc))
panic("Accessing user space memory outside uaccess.h routines");
}
/*
* As per x86, we may deadlock here. However, since the kernel only
@@ -561,3 +567,16 @@ void cpu_enable_pan(void *__unused)
config_sctlr_el1(SCTLR_EL1_SPAN, 0);
}
#endif /* CONFIG_ARM64_PAN */
#ifdef CONFIG_ARM64_UAO
/*
* Kernel threads have fs=KERNEL_DS by default, and don't need to call
* set_fs(), devtmpfs in particular relies on this behaviour.
* We need to enable the feature at runtime (instead of adding it to
* PSR_MODE_EL1h) as the feature may not be implemented by the cpu.
*/
void cpu_enable_uao(void *__unused)
{
asm(SET_PSTATE_UAO(1));
}
#endif /* CONFIG_ARM64_UAO */