While developing kasan for 64-bit book3s, I hit the following stack
over-read.
It occurs because the hypercall to put characters onto the terminal
takes 2 longs (128 bits/16 bytes) of characters at a time, and so
hvc_put_chars would unconditionally copy 16 bytes from the argument
buffer, regardless of supplied length. However, udbg_hvc_putc can
call hvc_put_chars with a single-byte buffer, leading to the error.
[ 0.001931]
==================================================================
[150/819]
[ 0.001933] BUG: KASAN: stack-out-of-bounds in hvc_put_chars+0xdc/0x110
[ 0.001934] Read of size 8 at addr c0000000023e7a90 by task swapper/0
[ 0.001934]
[ 0.001935] CPU: 0 PID: 0 Comm: swapper Not tainted
5.2.0-rc2-next-20190528-02824-g048a6ab4835b #113
[ 0.001935] Call Trace:
[ 0.001936] [c0000000023e7790] [c000000001b4a450] dump_stack+0x104/0x154
(unreliable)
[ 0.001937] [c0000000023e77f0] [c0000000006d3524]
print_address_description+0xa0/0x30c
[ 0.001938] [c0000000023e7880] [c0000000006d318c] __kasan_report+0x20c/0x224
[ 0.001939] [c0000000023e7950] [c0000000006d19d8] kasan_report+0x18/0x30
[ 0.001940] [c0000000023e7970] [c0000000006d4854]
__asan_report_load8_noabort+0x24/0x40
[ 0.001941] [c0000000023e7990] [c0000000001511ac] hvc_put_chars+0xdc/0x110
[ 0.001942] [c0000000023e7a10] [c000000000f81cfc]
hvterm_raw_put_chars+0x9c/0x110
[ 0.001943] [c0000000023e7a50] [c000000000f82634] udbg_hvc_putc+0x154/0x200
[ 0.001944] [c0000000023e7b10] [c000000000049c90] udbg_write+0xf0/0x240
[ 0.001945] [c0000000023e7b70] [c0000000002e5d88] console_unlock+0x868/0xd30
[ 0.001946] [c0000000023e7ca0] [c0000000002e6e00]
register_console+0x970/0xe90
[ 0.001947] [c0000000023e7d80] [c000000001ff1928]
register_early_udbg_console+0xf8/0x114
[ 0.001948] [c0000000023e7df0] [c000000001ff1174] setup_arch+0x108/0x790
[ 0.001948] [c0000000023e7e90] [c000000001fe41c8] start_kernel+0x104/0x784
[ 0.001949] [c0000000023e7f90] [c00000000000b368]
start_here_common+0x1c/0x534
[ 0.001950]
[ 0.001950]
[ 0.001951] Memory state around the buggy address:
[ 0.001952] c0000000023e7980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00
[ 0.001952] c0000000023e7a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f1
f1
[ 0.001953] >c0000000023e7a80: f1 f1 01 f2 f2 f2 00 00 00 00 00 00 00 00 00
00
[ 0.001953] ^
[ 0.001954] c0000000023e7b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00
[ 0.001954] c0000000023e7b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00
[ 0.001955]
==================================================================
Document that a 16-byte buffer is requred, and provide it in udbg.
CC: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: Daniel Axtens <d...@axtens.net>
---
v2: avoid memcpy, push responsibility to caller.
Solution suggested by mpe.
---
arch/powerpc/platforms/pseries/hvconsole.c | 2 +-
drivers/tty/hvc/hvc_vio.c | 16 +++++++++++++++-
2 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/hvconsole.c
b/arch/powerpc/platforms/pseries/hvconsole.c
index 74da18de853a..73ec15cd2708 100644
--- a/arch/powerpc/platforms/pseries/hvconsole.c
+++ b/arch/powerpc/platforms/pseries/hvconsole.c
@@ -62,7 +62,7 @@ EXPORT_SYMBOL(hvc_get_chars);
* @vtermno: The vtermno or unit_address of the adapter from which the data
* originated.
* @buf: The character buffer that contains the character data to send to
- * firmware.
+ * firmware. Must be at least 16 bytes, even if count is less than 16.
* @count: Send this number of characters.
*/
int hvc_put_chars(uint32_t vtermno, const char *buf, int count)
diff --git a/drivers/tty/hvc/hvc_vio.c b/drivers/tty/hvc/hvc_vio.c
index 6de6d4a1a221..7af54d6ed5b8 100644
--- a/drivers/tty/hvc/hvc_vio.c
+++ b/drivers/tty/hvc/hvc_vio.c
@@ -107,6 +107,14 @@ static int hvterm_raw_get_chars(uint32_t vtermno, char
*buf, int count)
return got;
}
+/**
+ * hvterm_raw_put_chars: send characters to firmware for given vterm adapter
+ * @vtermno: The virtual terminal number.
+ * @buf: The characters to send. Because of the underlying hypercall in
+ * hvc_put_chars(), this buffer must be at least 16 bytes long, even if
+ * you are sending fewer chars.
+ * @count: number of chars to send.
+ */
static int hvterm_raw_put_chars(uint32_t vtermno, const char *buf, int count)
{
struct hvterm_priv *pv = hvterm_privs[vtermno];
@@ -219,6 +227,7 @@ static const struct hv_ops hvterm_hvsi_ops = {
static void udbg_hvc_putc(char c)
{
int count = -1;
+ unsigned char bounce_buffer[16];
if (!hvterm_privs[0])
return;
@@ -229,7 +238,12 @@ static void udbg_hvc_putc(char c)
do {
switch(hvterm_privs[0]->proto) {
case HV_PROTOCOL_RAW:
- count = hvterm_raw_put_chars(0, &c, 1);
+ /*
+ * hvterm_raw_put_chars requires at least a 16-byte
+ * buffer, so go via the bounce buffer
+ */
+ bounce_buffer[0] = c;
+ count = hvterm_raw_put_chars(0, bounce_buffer, 1);
break;
case HV_PROTOCOL_HVSI:
count = hvterm_hvsi_put_chars(0, &c, 1);
--
2.19.1
