Tegra: spe: uninit console on a timeout

There are chances a denial-of-service attack, if an attacker
removes the SPE firmware from the system. The console driver
would end up waiting for the firmware to respond indefinitely.
The console driver must detect such scenarios and uninit the
interface as a result.

This patch adds a timeout to the interaction with the SPE
firmware and uninits the interface if it times out.

Change-Id: I06f27a858baed25711d41105b4110865f1a01727
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

diff --git a/plat/nvidia/tegra/common/drivers/spe/shared_console.S b/plat/nvidia/tegra/common/drivers/spe/shared_console.S
index a3e110ec98d2c67e7f74f255265c0d421eb22e8f..0be34e41732ab225202cff364b8b99344d35e529 100644 (file)
--- a/plat/nvidia/tegra/common/drivers/spe/shared_console.S
+++ b/plat/nvidia/tegra/common/drivers/spe/shared_console.S
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2020, NVIDIA Corporation. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -10,6 +11,7 @@
 #define CONSOLE_FLUSH_DATA_TO_PORT     (1 << 26)
 #define CONSOLE_RING_DOORBELL          (1 << 31)
 #define CONSOLE_IS_BUSY                        (1 << 31)
+#define CONSOLE_TIMEOUT                        0xC000          /* approx. 50 ms */
 #define CONSOLE_WRITE                  (CONSOLE_RING_DOORBELL | CONSOLE_FLUSH_DATA_TO_PORT)
 
        /*
@@ -30,6 +32,20 @@
        .globl  console_spe_flush
        .globl  console_spe_register
 
+.macro check_if_console_is_ready base, tmp1, tmp2, label
+       /* wait until spe is ready or timeout expires */
+       mrs     \tmp2, cntps_tval_el1
+1:     ldr     \tmp1, [\base]
+       and     \tmp1, \tmp1, #CONSOLE_IS_BUSY
+       cbz     \tmp1, 2f
+       mrs     \tmp1, cntps_tval_el1
+       sub     \tmp1, \tmp2, \tmp1
+       cmp     \tmp1, #CONSOLE_TIMEOUT
+       b.lt    1b
+       b       \label
+2:
+.endm
+
        /* -------------------------------------------------
         * int console_spe_register(uintptr_t baseaddr,
         *     uint32_t clock, uint32_t baud,
@@ -46,6 +62,12 @@
         * -------------------------------------------------
         */
 func console_spe_register
+       /* Check the input base address */
+       cbz     x0, register_fail
+
+       /* Dont use clock or baud rate, so ok to overwrite them */
+       check_if_console_is_ready x0, x1, x2, register_fail
+
        cbz     x3, register_fail
        str     x0, [x3, #CONSOLE_T_DRVDATA]
        mov     x0, x3
@@ -63,7 +85,7 @@ endfunc console_spe_register
         * In : w0 - character to be printed
         *      x1 - console base address
         * Out : return -1 on error else return character.
-        * Clobber list : x2
+        * Clobber list : x2, x3
         * --------------------------------------------------------
         */
 func console_spe_core_putc
@@ -72,12 +94,9 @@ func console_spe_core_putc
 
        /* Prepend '\r' to '\n' */
        cmp     w0, #0xA
-       b.ne    2f
+       b.ne    not_eol
 
-       /* wait until spe is ready */
-1:     ldr     w2, [x1]
-       and     w2, w2, #CONSOLE_IS_BUSY
-       cbnz    w2, 1b
+       check_if_console_is_ready x1, x2, x3, putc_error
 
        /* spe is ready */
        mov     w2, #0xD                /* '\r' */
@@ -86,10 +105,8 @@ func console_spe_core_putc
        orr     w2, w2, w3
        str     w2, [x1]
 
-       /* wait until spe is ready */
-2:     ldr     w2, [x1]
-       and     w2, w2, #CONSOLE_IS_BUSY
-       cbnz    w2, 2b
+not_eol:
+       check_if_console_is_ready x1, x2, x3, putc_error
 
        /* spe is ready */
        mov     w2, w0