| Message ID | 20240702155752.3022007-1-zheyuma97@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] hw/char/pl011: Avoid division-by-zero in pl011_get_baudrate() | expand |
On 2/7/24 17:57, Zheyu Ma wrote: > In pl011_get_baudrate(), when we calculate the baudrate we can > accidentally divide by zero. This happens because although (as the > specification requires) we treat UARTIBRD = 0 as invalid, we aren't > correctly limiting UARTIBRD and UARTFBRD values to the 16-bit and 6-bit > ranges the hardware allows, and so some non-zero values of UARTIBRD can > result in a zero divisor. > > Enforce the correct register field widths on guest writes and on inbound > migration to avoid the division by zero. > > ASAN log: > ==2973125==ERROR: AddressSanitizer: FPE on unknown address 0x55f72629b348 > (pc 0x55f72629b348 bp 0x7fffa24d0e00 sp 0x7fffa24d0d60 T0) > #0 0x55f72629b348 in pl011_get_baudrate hw/char/pl011.c:255:17 > #1 0x55f726298d94 in pl011_trace_baudrate_change hw/char/pl011.c:260:33 > #2 0x55f726296fc8 in pl011_write hw/char/pl011.c:378:9 > > Reproducer: > cat << EOF | qemu-system-aarch64 -display \ > none -machine accel=qtest, -m 512M -machine realview-pb-a8 -qtest stdio > writeq 0x1000b024 0xf8000000 > EOF > > Suggested-by: Philippe Mathieu-Daudé <philmd@linaro.org> Peter, feel free to replace that line by: Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> > Suggested-by: Peter Maydell <peter.maydell@linaro.org> > Signed-off-by: Zheyu Ma <zheyuma97@gmail.com> > --- > Changes in v3: > - Defined masks for UARTIBRD and UARTFBRD to avoid magic numbers. Thanks Zheyu! > Changes in v2: > - Enforce the correct register field widths on writes to both UARTIBRD > and UARTFBRD registers. > - Mask UARTIBRD to 16 bits and UARTFBRD to 6 bits in the pl011_post_load > function to prevent division by zero during inbound migration. > --- > hw/char/pl011.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-)
On Tue, 2 Jul 2024 at 17:18, Philippe Mathieu-Daudé <philmd@linaro.org> wrote: > > On 2/7/24 17:57, Zheyu Ma wrote: > > In pl011_get_baudrate(), when we calculate the baudrate we can > > accidentally divide by zero. This happens because although (as the > > specification requires) we treat UARTIBRD = 0 as invalid, we aren't > > correctly limiting UARTIBRD and UARTFBRD values to the 16-bit and 6-bit > > ranges the hardware allows, and so some non-zero values of UARTIBRD can > > result in a zero divisor. > > > > Enforce the correct register field widths on guest writes and on inbound > > migration to avoid the division by zero. > > > > ASAN log: > > ==2973125==ERROR: AddressSanitizer: FPE on unknown address 0x55f72629b348 > > (pc 0x55f72629b348 bp 0x7fffa24d0e00 sp 0x7fffa24d0d60 T0) > > #0 0x55f72629b348 in pl011_get_baudrate hw/char/pl011.c:255:17 > > #1 0x55f726298d94 in pl011_trace_baudrate_change hw/char/pl011.c:260:33 > > #2 0x55f726296fc8 in pl011_write hw/char/pl011.c:378:9 > > > > Reproducer: > > cat << EOF | qemu-system-aarch64 -display \ > > none -machine accel=qtest, -m 512M -machine realview-pb-a8 -qtest stdio > > writeq 0x1000b024 0xf8000000 > > EOF > > > > Suggested-by: Philippe Mathieu-Daudé <philmd@linaro.org> > > Peter, feel free to replace that line by: > Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> OK; applied to target-arm.next, thanks. -- PMM
diff --git a/hw/char/pl011.c b/hw/char/pl011.c index 8753b84a84..f8078aa216 100644 --- a/hw/char/pl011.c +++ b/hw/char/pl011.c @@ -87,6 +87,12 @@ DeviceState *pl011_create(hwaddr addr, qemu_irq irq, Chardev *chr) #define CR_DTR (1 << 10) #define CR_LBE (1 << 7) +/* Integer Baud Rate Divider, UARTIBRD */ +#define IBRD_MASK 0x3f + +/* Fractional Baud Rate Divider, UARTFBRD */ +#define FBRD_MASK 0xffff + static const unsigned char pl011_id_arm[8] = { 0x11, 0x10, 0x14, 0x00, 0x0d, 0xf0, 0x05, 0xb1 }; static const unsigned char pl011_id_luminary[8] = @@ -374,11 +380,11 @@ static void pl011_write(void *opaque, hwaddr offset, s->ilpr = value; break; case 9: /* UARTIBRD */ - s->ibrd = value; + s->ibrd = value & IBRD_MASK; pl011_trace_baudrate_change(s); break; case 10: /* UARTFBRD */ - s->fbrd = value; + s->fbrd = value & FBRD_MASK; pl011_trace_baudrate_change(s); break; case 11: /* UARTLCR_H */ @@ -531,6 +537,9 @@ static int pl011_post_load(void *opaque, int version_id) s->read_pos = 0; } + s->ibrd &= IBRD_MASK; + s->fbrd &= FBRD_MASK; + return 0; }
In pl011_get_baudrate(), when we calculate the baudrate we can accidentally divide by zero. This happens because although (as the specification requires) we treat UARTIBRD = 0 as invalid, we aren't correctly limiting UARTIBRD and UARTFBRD values to the 16-bit and 6-bit ranges the hardware allows, and so some non-zero values of UARTIBRD can result in a zero divisor. Enforce the correct register field widths on guest writes and on inbound migration to avoid the division by zero. ASAN log: ==2973125==ERROR: AddressSanitizer: FPE on unknown address 0x55f72629b348 (pc 0x55f72629b348 bp 0x7fffa24d0e00 sp 0x7fffa24d0d60 T0) #0 0x55f72629b348 in pl011_get_baudrate hw/char/pl011.c:255:17 #1 0x55f726298d94 in pl011_trace_baudrate_change hw/char/pl011.c:260:33 #2 0x55f726296fc8 in pl011_write hw/char/pl011.c:378:9 Reproducer: cat << EOF | qemu-system-aarch64 -display \ none -machine accel=qtest, -m 512M -machine realview-pb-a8 -qtest stdio writeq 0x1000b024 0xf8000000 EOF Suggested-by: Philippe Mathieu-Daudé <philmd@linaro.org> Suggested-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com> --- Changes in v3: - Defined masks for UARTIBRD and UARTFBRD to avoid magic numbers. Changes in v2: - Enforce the correct register field widths on writes to both UARTIBRD and UARTFBRD registers. - Mask UARTIBRD to 16 bits and UARTFBRD to 6 bits in the pl011_post_load function to prevent division by zero during inbound migration. --- hw/char/pl011.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)