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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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72
arch/arm64/include/asm/alternative.h
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@@ -1,6 +1,8 @@
#ifndef __ASM_ALTERNATIVE_H
#define __ASM_ALTERNATIVE_H
#include <asm/cpufeature.h>
#ifndef __ASSEMBLY__
#include <linux/init.h>
@@ -63,6 +65,8 @@ void apply_alternatives(void *start, size_t length);
#else
#include <asm/assembler.h>
.macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
.word \orig_offset - .
.word \alt_offset - .
@@ -136,6 +140,74 @@ void apply_alternatives(void *start, size_t length);
alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
/*
* Generate the assembly for UAO alternatives with exception table entries.
* This is complicated as there is no post-increment or pair versions of the
* unprivileged instructions, and USER() only works for single instructions.
*/
#ifdef CONFIG_ARM64_UAO
.macro uao_ldp l, reg1, reg2, addr, post_inc
alternative_if_not ARM64_HAS_UAO
8888: ldp \reg1, \reg2, [\addr], \post_inc;
8889: nop;
nop;
alternative_else
ldtr \reg1, [\addr];
ldtr \reg2, [\addr, #8];
add \addr, \addr, \post_inc;
alternative_endif
.section __ex_table,"a";
.align 3;
.quad 8888b,\l;
.quad 8889b,\l;
.previous;
.endm
.macro uao_stp l, reg1, reg2, addr, post_inc
alternative_if_not ARM64_HAS_UAO
8888: stp \reg1, \reg2, [\addr], \post_inc;
8889: nop;
nop;
alternative_else
sttr \reg1, [\addr];
sttr \reg2, [\addr, #8];
add \addr, \addr, \post_inc;
alternative_endif
.section __ex_table,"a";
.align 3;
.quad 8888b,\l;
.quad 8889b,\l;
.previous
.endm
.macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
alternative_if_not ARM64_HAS_UAO
8888: \inst \reg, [\addr], \post_inc;
nop;
alternative_else
\alt_inst \reg, [\addr];
add \addr, \addr, \post_inc;
alternative_endif
.section __ex_table,"a";
.align 3;
.quad 8888b,\l;
.previous
.endm
#else
.macro uao_ldp l, reg1, reg2, addr, post_inc
USER(\l, ldp \reg1, \reg2, [\addr], \post_inc)
.endm
.macro uao_stp l, reg1, reg2, addr, post_inc
USER(\l, stp \reg1, \reg2, [\addr], \post_inc)
.endm
.macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
USER(\l, \inst \reg, [\addr], \post_inc)
.endm
#endif
#endif /* __ASSEMBLY__ */
/*