BACKPORT: arm64: kernel: Save and restore UAO and addr_limit on exception entry

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.

Cc: <stable@vger.kernel.org> # 4.6-
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>
Change-Id: Iab453201c6e08bc6e22500b7c5570dd0fe2d1b74
(cherry picked from commit e19a6ee2460bdd0d0055a6029383422773f9999a)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index e9e5467..200d5c3 100644 (file)
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -116,6 +116,8 @@ struct pt_regs {
        };
        u64 orig_x0;
        u64 syscallno;
+       u64 orig_addr_limit;
+       u64 unused;     // maintain 16 byte alignment
 };
 
 #define arch_has_single_step() (1)

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 25de8b2..087cf9a 100644 (file)
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -58,6 +58,7 @@ 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));

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index eefffa8..9fabed5 100644 (file)
--- 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

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 56c6bfb..03d4438 100644 (file)
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -287,7 +287,8 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
        }
 
        if (is_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))