arm64: entry: improve data abort handling of tagged pointers

When handling a data abort from EL0, we currently zero the top byte of
the faulting address, as we assume the address is a TTBR0 address, which
may contain a non-zero address tag. However, the address may be a TTBR1
address, in which case we should not zero the top byte. This patch fixes
that. The effect is that the full TTBR1 address is passed to the task's
signal handler (or printed out in the kernel log).

When handling a data abort from EL1, we leave the faulting address
intact, as we assume it's either a TTBR1 address or a TTBR0 address with
tag 0x00. This is true as far as I'm aware, we don't seem to access a
tagged TTBR0 address anywhere in the kernel. Regardless, it's easy to
forget about address tags, and code added in the future may not always
remember to remove tags from addresses before accessing them. So add tag
handling to the EL1 data abort handler as well. This also makes it
consistent with the EL0 data abort handler.

Fixes: d50240a5f6ce ("arm64: mm: permit use of tagged pointers at EL0")
Cc: <stable@vger.kernel.org> # 3.12.x-
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
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>

diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
index df411f3e083ce7074daedf65c8bb3ed4aed4dc31..ecd9788cd29881074dd04bb9708eddef286677a6 100644 (file)
--- a/arch/arm64/include/asm/asm-uaccess.h
+++ b/arch/arm64/include/asm/asm-uaccess.h
@@ -62,4 +62,13 @@ alternative_if ARM64_ALT_PAN_NOT_UAO
 alternative_else_nop_endif
        .endm
 
+/*
+ * Remove the address tag from a virtual address, if present.
+ */
+       .macro  clear_address_tag, dst, addr
+       tst     \addr, #(1 << 55)
+       bic     \dst, \addr, #(0xff << 56)
+       csel    \dst, \dst, \addr, eq
+       .endm
+
 #endif

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 43512d4d7df219b4b7093927fc1d9107004b6775..b738880350f9e43b8e2f3234210bda153586caf5 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -428,12 +428,13 @@ el1_da:
        /*
         * Data abort handling
         */
-       mrs     x0, far_el1
+       mrs     x3, far_el1
        enable_dbg
        // re-enable interrupts if they were enabled in the aborted context
        tbnz    x23, #7, 1f                     // PSR_I_BIT
        enable_irq
 1:
+       clear_address_tag x0, x3
        mov     x2, sp                          // struct pt_regs
        bl      do_mem_abort
 
@@ -594,7 +595,7 @@ el0_da:
        // enable interrupts before calling the main handler
        enable_dbg_and_irq
        ct_user_exit
-       bic     x0, x26, #(0xff << 56)
+       clear_address_tag x0, x26
        mov     x1, x25
        mov     x2, sp
        bl      do_mem_abort