[PATCH 4.6 099/203] arm64: kernel: Save and restore UAO and addr_limit on exception entry

Greg Kroah-Hartman
2016-07-25T21:33:54Z

From: James Morse <james.morse@arm.com>

commit e19a6ee2460bdd0d0055a6029383422773f9999a upstream.

If we take an exception while at EL1, the exception handler inherits
the original context's addr_limit and PSTATE.UAO values. To be consistent
always reset addr_limit and PSTATE.UAO on (re-)entry to EL1. This
prevents accidental re-use of the original context's addr_limit.

Based on a similar patch for arm from Russell King.

Acked-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/include/asm/ptrace.h | 2 ++
arch/arm64/kernel/asm-offsets.c | 1 +
arch/arm64/kernel/entry.S | 19 +++++++++++++++++--
arch/arm64/mm/fault.c | 3 ++-
4 files changed, 22 insertions(+), 3 deletions(-)

--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -117,6 +117,8 @@ struct pt_regs {
};
u64 orig_x0;
u64 syscallno;
+ u64 orig_addr_limit;
+ u64 unused; // maintain 16 byte alignment
};

#define arch_has_single_step() (1)
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -59,6 +59,7 @@ int main(void)
DEFINE(S_PC, offsetof(struct pt_regs, pc));
DEFINE(S_ORIG_X0, offsetof(struct pt_regs, orig_x0));
DEFINE(S_SYSCALLNO, offsetof(struct pt_regs, syscallno));
+ DEFINE(S_ORIG_ADDR_LIMIT, offsetof(struct pt_regs, orig_addr_limit));
DEFINE(S_FRAME_SIZE, sizeof(struct pt_regs));
BLANK();
DEFINE(MM_CONTEXT_ID, offsetof(struct mm_struct, context.id.counter));
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -28,6 +28,7 @@
#include <asm/errno.h>
#include <asm/esr.h>
#include <asm/irq.h>
+#include <asm/memory.h>
#include <asm/thread_info.h>
#include <asm/unistd.h>

@@ -97,7 +98,14 @@
mov x29, xzr // fp pointed to user-space
.else
add x21, sp, #S_FRAME_SIZE
- .endif
+ get_thread_info tsk
+ /* Save the task's original addr_limit and set USER_DS (TASK_SIZE_64) */
+ ldr x20, [tsk, #TI_ADDR_LIMIT]
+ str x20, [sp, #S_ORIG_ADDR_LIMIT]
+ mov x20, #TASK_SIZE_64
+ str x20, [tsk, #TI_ADDR_LIMIT]
+ ALTERNATIVE(nop, SET_PSTATE_UAO(0), ARM64_HAS_UAO, CONFIG_ARM64_UAO)
+ .endif /* \el == 0 */
mrs x22, elr_el1
mrs x23, spsr_el1
stp lr, x21, [sp, #S_LR]
@@ -128,6 +136,14 @@
.endm

.macro kernel_exit, el
+ .if \el != 0
+ /* Restore the task's original addr_limit. */
+ ldr x20, [sp, #S_ORIG_ADDR_LIMIT]
+ str x20, [tsk, #TI_ADDR_LIMIT]
+
+ /* No need to restore UAO, it will be restored from SPSR_EL1 */
+ .endif
+
ldp x21, x22, [sp, #S_PC] // load ELR, SPSR
.if \el == 0
ct_user_enter
@@ -406,7 +422,6 @@ el1_irq:
bl trace_hardirqs_off
#endif

- get_thread_info tsk
irq_handler

#ifdef CONFIG_PREEMPT
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -284,7 +284,8 @@ static int __kprobes do_page_fault(unsig
}

if (permission_fault(esr) && (addr < USER_DS)) {
- if (get_fs() == KERNEL_DS)
+ /* regs->orig_addr_limit may be 0 if we entered from EL0 */
+ if (regs->orig_addr_limit == KERNEL_DS)
die("Accessing user space memory with fs=KERNEL_DS", regs, esr);

if (!search_exception_tables(regs->pc))