| Message ID | alpine.DEB.2.21.2105181508460.3032@angie.orcam.me.uk |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] serial: 8250: Mask out floating 16/32-bit bus bits | expand |
On 10. 06. 21, 20:38, Maciej W. Rozycki wrote: > Make sure only actual 8 bits of the IIR register are used in determining > the port type in `autoconfig'. > > The `serial_in' port accessor returns the `unsigned int' type, meaning > that with UPIO_AU, UPIO_MEM16, UPIO_MEM32, and UPIO_MEM32BE access types > more than 8 bits of data are returned, of which the high order bits will > often come from bus lines that are left floating in the data phase. For > example with the MIPS Malta board's CBUS UART, where the registers are > aligned on 8-byte boundaries and which uses 32-bit accesses, data as > follows is returned: > > YAMON> dump -32 0xbf000900 0x40 > > BF000900: 1F000942 1F000942 1F000900 1F000900 ...B...B........ > BF000910: 1F000901 1F000901 1F000900 1F000900 ................ > BF000920: 1F000900 1F000900 1F000960 1F000960 ...........`...` > BF000930: 1F000900 1F000900 1F0009FF 1F0009FF ................ > > YAMON> > > Evidently high-order 24 bits return values previously driven in the > address phase (the 3 highest order address bits used with the command > above are masked out in the simple virtual address mapping used here and > come out at zeros on the external bus), a common scenario with bus lines > left floating, due to bus capacitance. > > Consequently when the value of IIR, mapped at 0x1f000910, is retrieved > in `autoconfig', it comes out at 0x1f0009c1 and when it is right-shifted > by 6 and then assigned to 8-bit `scratch' variable, the value calculated > is 0x27, not one of 0, 1, 2, 3 expected in port type determination. > > Fix the issue then, by assigning the value returned from `serial_in' to > `scratch' first, which masks out 24 high-order bits retrieved, and only > then right-shift the resulting 8-bit data quantity, producing the value > of 3 in this case, as expected. Fix the same issue in `serial_dl_read'. > > The problem first appeared with Linux 2.6.9-rc3 which predates our repo > history, but the origin could be identified with the old MIPS/Linux repo > also at: <git://git.kernel.org/pub/scm/linux/kernel/git/ralf/linux.git> > as commit e0d2356c0777 ("Merge with Linux 2.6.9-rc3."), where code in > `serial_in' was updated with this case: > > + case UPIO_MEM32: > + return readl(up->port.membase + offset); > + > > which made it produce results outside the unsigned 8-bit range for the > first time, though obviously it is system dependent what actual values > appear in the high order bits retrieved and it may well have been zeros > in the relevant positions with the system the change originally was > intended for. It is at that point that code in `autoconf' should have > been updated accordingly, but clearly it was overlooked. > > Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > --- > drivers/tty/serial/8250/8250_port.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > linux-serial-8250-floating-bus-mask.diff > Index: linux-malta-cbus-uart/drivers/tty/serial/8250/8250_port.c > =================================================================== > --- linux-malta-cbus-uart.orig/drivers/tty/serial/8250/8250_port.c > +++ linux-malta-cbus-uart/drivers/tty/serial/8250/8250_port.c > @@ -311,7 +311,10 @@ static const struct serial8250_config ua > /* Uart divisor latch read */ > static int default_serial_dl_read(struct uart_8250_port *up) > { > - return serial_in(up, UART_DLL) | serial_in(up, UART_DLM) << 8; > + unsigned char dll = serial_in(up, UART_DLL); > + unsigned char dlm = serial_in(up, UART_DLM); > + > + return dll | dlm << 8; > } > > /* Uart divisor latch write */ > @@ -1297,9 +1300,9 @@ static void autoconfig(struct uart_8250_ > serial_out(up, UART_LCR, 0); > > serial_out(up, UART_FCR, UART_FCR_ENABLE_FIFO); > - scratch = serial_in(up, UART_IIR) >> 6; > + scratch = serial_in(up, UART_IIR); > > - switch (scratch) { > + switch (scratch >> 6) { COrrect, but not obvious on the first look. People could revert this change inadverently. So could you add a comment, or simply cast serial_in() output to (u8)? > case 0: > autoconfig_8250(up); > break; > thanks, -- js suse labs
On Fri, Jun 11, 2021 at 09:40:31AM +0300, Andy Shevchenko wrote: > On Thursday, June 10, 2021, Maciej W. Rozycki <macro@orcam.me.uk> wrote: > > Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> > > Fixes: 1da177e4c3f4 ("Linux-2.6.12- > > > Please, find the history group repository (Git.kernel.org) and use proper > hash of the real commit. There is no real need to do that, I'll just put a "cc: stable" in here and it will go back as far as we currently maintain. thanks, greg k-h
On Thu, Jun 10, 2021 at 8:39 PM Maciej W. Rozycki <macro@orcam.me.uk> wrote: > > Make sure only actual 8 bits of the IIR register are used in determining > the port type in `autoconfig'. > > The `serial_in' port accessor returns the `unsigned int' type, meaning > that with UPIO_AU, UPIO_MEM16, UPIO_MEM32, and UPIO_MEM32BE access types > more than 8 bits of data are returned, of which the high order bits will > often come from bus lines that are left floating in the data phase. For > example with the MIPS Malta board's CBUS UART, where the registers are > aligned on 8-byte boundaries and which uses 32-bit accesses, data as > follows is returned: > > YAMON> dump -32 0xbf000900 0x40 > > BF000900: 1F000942 1F000942 1F000900 1F000900 ...B...B........ > BF000910: 1F000901 1F000901 1F000900 1F000900 ................ > BF000920: 1F000900 1F000900 1F000960 1F000960 ...........`...` > BF000930: 1F000900 1F000900 1F0009FF 1F0009FF ................ > > YAMON> > > Evidently high-order 24 bits return values previously driven in the > address phase (the 3 highest order address bits used with the command > above are masked out in the simple virtual address mapping used here and > come out at zeros on the external bus), a common scenario with bus lines > left floating, due to bus capacitance. > > Consequently when the value of IIR, mapped at 0x1f000910, is retrieved > in `autoconfig', it comes out at 0x1f0009c1 and when it is right-shifted > by 6 and then assigned to 8-bit `scratch' variable, the value calculated > is 0x27, not one of 0, 1, 2, 3 expected in port type determination. > > Fix the issue then, by assigning the value returned from `serial_in' to > `scratch' first, which masks out 24 high-order bits retrieved, and only > then right-shift the resulting 8-bit data quantity, producing the value > of 3 in this case, as expected. Fix the same issue in `serial_dl_read'. > > The problem first appeared with Linux 2.6.9-rc3 which predates our repo > history, but the origin could be identified with the old MIPS/Linux repo > also at: <git://git.kernel.org/pub/scm/linux/kernel/git/ralf/linux.git> > as commit e0d2356c0777 ("Merge with Linux 2.6.9-rc3."), where code in > `serial_in' was updated with this case: > > + case UPIO_MEM32: > + return readl(up->port.membase + offset); > + > > which made it produce results outside the unsigned 8-bit range for the > first time, though obviously it is system dependent what actual values > appear in the high order bits retrieved and it may well have been zeros > in the relevant positions with the system the change originally was > intended for. It is at that point that code in `autoconf' should have > been updated accordingly, but clearly it was overlooked. > > Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > --- > drivers/tty/serial/8250/8250_port.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
On Fri, 11 Jun 2021, Greg Kroah-Hartman wrote: > On Fri, Jun 11, 2021 at 09:40:31AM +0300, Andy Shevchenko wrote: > > > Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> > > > Fixes: 1da177e4c3f4 ("Linux-2.6.12- > > > > > > Please, find the history group repository (Git.kernel.org) and use proper > > hash of the real commit. Thanks for making me aware of that repo, it can be helpful. > There is no real need to do that, I'll just put a "cc: stable" in here > and it will go back as far as we currently maintain. I've posted v2 then, with Jiri's concern addressed and a "cc: stable" annotation. Originally I didn't think this series is worth backporting, but if you'd rather do so, then of course I'm fine with that. Maciej
Index: linux-malta-cbus-uart/drivers/tty/serial/8250/8250_port.c =================================================================== --- linux-malta-cbus-uart.orig/drivers/tty/serial/8250/8250_port.c +++ linux-malta-cbus-uart/drivers/tty/serial/8250/8250_port.c @@ -311,7 +311,10 @@ static const struct serial8250_config ua /* Uart divisor latch read */ static int default_serial_dl_read(struct uart_8250_port *up) { - return serial_in(up, UART_DLL) | serial_in(up, UART_DLM) << 8; + unsigned char dll = serial_in(up, UART_DLL); + unsigned char dlm = serial_in(up, UART_DLM); + + return dll | dlm << 8; } /* Uart divisor latch write */ @@ -1297,9 +1300,9 @@ static void autoconfig(struct uart_8250_ serial_out(up, UART_LCR, 0); serial_out(up, UART_FCR, UART_FCR_ENABLE_FIFO); - scratch = serial_in(up, UART_IIR) >> 6; + scratch = serial_in(up, UART_IIR); - switch (scratch) { + switch (scratch >> 6) { case 0: autoconfig_8250(up); break;
Make sure only actual 8 bits of the IIR register are used in determining the port type in `autoconfig'. The `serial_in' port accessor returns the `unsigned int' type, meaning that with UPIO_AU, UPIO_MEM16, UPIO_MEM32, and UPIO_MEM32BE access types more than 8 bits of data are returned, of which the high order bits will often come from bus lines that are left floating in the data phase. For example with the MIPS Malta board's CBUS UART, where the registers are aligned on 8-byte boundaries and which uses 32-bit accesses, data as follows is returned: YAMON> dump -32 0xbf000900 0x40 BF000900: 1F000942 1F000942 1F000900 1F000900 ...B...B........ BF000910: 1F000901 1F000901 1F000900 1F000900 ................ BF000920: 1F000900 1F000900 1F000960 1F000960 ...........`...` BF000930: 1F000900 1F000900 1F0009FF 1F0009FF ................ YAMON> Evidently high-order 24 bits return values previously driven in the address phase (the 3 highest order address bits used with the command above are masked out in the simple virtual address mapping used here and come out at zeros on the external bus), a common scenario with bus lines left floating, due to bus capacitance. Consequently when the value of IIR, mapped at 0x1f000910, is retrieved in `autoconfig', it comes out at 0x1f0009c1 and when it is right-shifted by 6 and then assigned to 8-bit `scratch' variable, the value calculated is 0x27, not one of 0, 1, 2, 3 expected in port type determination. Fix the issue then, by assigning the value returned from `serial_in' to `scratch' first, which masks out 24 high-order bits retrieved, and only then right-shift the resulting 8-bit data quantity, producing the value of 3 in this case, as expected. Fix the same issue in `serial_dl_read'. The problem first appeared with Linux 2.6.9-rc3 which predates our repo history, but the origin could be identified with the old MIPS/Linux repo also at: <git://git.kernel.org/pub/scm/linux/kernel/git/ralf/linux.git> as commit e0d2356c0777 ("Merge with Linux 2.6.9-rc3."), where code in `serial_in' was updated with this case: + case UPIO_MEM32: + return readl(up->port.membase + offset); + which made it produce results outside the unsigned 8-bit range for the first time, though obviously it is system dependent what actual values appear in the high order bits retrieved and it may well have been zeros in the relevant positions with the system the change originally was intended for. It is at that point that code in `autoconf' should have been updated accordingly, but clearly it was overlooked. Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") --- drivers/tty/serial/8250/8250_port.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) linux-serial-8250-floating-bus-mask.diff