ASoC: Add bounds checking for written values

PATCH In review Mark Brown 3 participants 11 messages Jan 24, 2022 – Jan 25, 2022

Subsystems (3)

Stable branch Sound ASoC

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Mark Brown

author maintainer

2022-01-24 15:34 UTC #0 lore raw

cover ASoC: Add bounds checking for written values

This series adds verification that values written to registers are in bounds for controls since the core doesn't validate for us.

Mark Brown (3):
ASoC: ops: Reject out of bounds values in snd_soc_put_volsw()
ASoC: ops: Reject out of bounds values in snd_soc_put_volsw_sx()
ASoC: ops: Reject out of bounds values in snd_soc_put_xr_sx()

 sound/soc/soc-ops.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07

Signature · 1 line

2.30.2

Mark Brown

author maintainer

2022-01-24 15:33 UTC #1 lore raw

PATCH 1/3 ASoC: ops: Reject out of bounds values in snd_soc_put_volsw()

We don't currently validate that the values being set are within the range we advertised to userspace as being valid, do so and reject any values that are out of range.

Signed-off-by Mark Brown <[email protected]>

Cc [email protected]

---
 sound/soc/soc-ops.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

sound/soc/soc-ops.c +16 -2

index 08eaa9ddf191..fbe5d326b0f2 100644
@@ -316,13 +316,27 @@ int snd_soc_put_volsw(struct snd_kcontrol *kcontrol,
 	if (sign_bit)
 		mask = BIT(sign_bit + 1) - 1;
 
-	val = ((ucontrol->value.integer.value[0] + min) & mask);
+	val = ucontrol->value.integer.value[0];
+	if (mc->platform_max && val > mc->platform_max)
+		return -EINVAL;
+	if (val > max - min)
+		return -EINVAL;
+	if (val < 0)
+		return -EINVAL;
+	val = (val + min) & mask;
 	if (invert)
 		val = max - val;
 	val_mask = mask << shift;
 	val = val << shift;
 	if (snd_soc_volsw_is_stereo(mc)) {
-		val2 = ((ucontrol->value.integer.value[1] + min) & mask);
+		val2 = ucontrol->value.integer.value[1];
+		if (mc->platform_max && val2 > mc->platform_max)
+			return -EINVAL;
+		if (val2 > max - min)
+			return -EINVAL;
+		if (val2 < 0)
+			return -EINVAL;
+		val2 = (val2 + min) & mask;
 		if (invert)
 			val2 = max - val2;
 		if (reg == reg2) {

Signature · 1 line

2.30.2

Mark Brown

author maintainer

2022-01-24 15:33 UTC #2 lore raw

PATCH 2/3 ASoC: ops: Reject out of bounds values in snd_soc_put_volsw_sx()

In reply to Mark Brown

We don't currently validate that the values being set are within the range we advertised to userspace as being valid, do so and reject any values that are out of range.

Signed-off-by Mark Brown <[email protected]>

Cc [email protected]

---
 sound/soc/soc-ops.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

sound/soc/soc-ops.c +8 -1

index fbe5d326b0f2..c31e63b27193 100644
@@ -423,8 +423,15 @@ int snd_soc_put_volsw_sx(struct snd_kcontrol *kcontrol,
 	int err = 0;
 	unsigned int val, val_mask;
 
+	val = ucontrol->value.integer.value[0];
+	if (mc->platform_max && val > mc->platform_max)
+		return -EINVAL;
+	if (val > max - min)
+		return -EINVAL;
+	if (val < 0)
+		return -EINVAL;
 	val_mask = mask << shift;
-	val = (ucontrol->value.integer.value[0] + min) & mask;
+	val = (val + min) & mask;
 	val = val << shift;
 
 	err = snd_soc_component_update_bits(component, reg, val_mask, val);

Signature · 1 line

2.30.2

Mark Brown

author maintainer

2022-01-24 15:33 UTC #3 lore raw

PATCH 3/3 ASoC: ops: Reject out of bounds values in snd_soc_put_xr_sx()

In reply to Mark Brown

We don't currently validate that the values being set are within the range we advertised to userspace as being valid, do so and reject any values that are out of range.

Signed-off-by Mark Brown <[email protected]>

Cc [email protected]

---
 sound/soc/soc-ops.c | 2 ++
 1 file changed, 2 insertions(+)

sound/soc/soc-ops.c +2 -0

index c31e63b27193..dc0e7c8d31f3 100644
@@ -879,6 +879,8 @@ int snd_soc_put_xr_sx(struct snd_kcontrol *kcontrol,
 	long val = ucontrol->value.integer.value[0];
 	unsigned int i;
 
+	if (val < mc->min || val > mc->max)
+		return -EINVAL;
 	if (invert)
 		val = max - val;
 	val &= mask;

Signature · 1 line

2.30.2

Jaroslav Kysela

maintainer

2022-01-24 16:30 UTC #4 lore raw

In reply to Mark Brown

Quoted 2 lines · Mark Brown

This series adds verification that values written to registers are in bounds for controls since the core doesn't validate for us.

As discussed, those conditions should be optional to eventually catch the wrong applications. I don't see any benefit to report the range error back when there is value masking code already. The users will note when the unwanted values are written to the hardware, or not?

Thanks,
Jaroslav

Signature · 2 lines

Jaroslav Kysela <[email protected]>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

Mark Brown

author maintainer

2022-01-24 16:53 UTC #5 lore raw

Quoted 9 lines · Jaroslav Kysela

Quoted 2 lines · Mark Brown
This series adds verification that values written to registers are in bounds for controls since the core doesn't validate for us.
As discussed, those conditions should be optional to eventually catch the wrong applications. I don't see any benefit to report the range error back when there is value masking code already. The users will note when the unwanted values are written to the hardware, or not?

In general I'd say that silent failures are harder to work with than returning an error at the point where we notice that there's a problem, assuming userspace is paying any attention to the error return at all of course. We certainly have quite a lot of existing put() methods that do return errors and it's not like the application isn't invoking undefined behaviour so I don't see a problem here.

Takashi Iwai

2022-01-24 17:09 UTC #6 lore raw

Quoted 12 lines · Mark Brown

Quoted 9 lines · Jaroslav Kysela
Quoted 2 lines · Mark Brown
This series adds verification that values written to registers are in bounds for controls since the core doesn't validate for us.
As discussed, those conditions should be optional to eventually catch the wrong applications. I don't see any benefit to report the range error back when there is value masking code already. The users will note when the unwanted values are written to the hardware, or not?

Quoted 6 lines

In general I'd say that silent failures are harder to work with than returning an error at the point where we notice that there's a problem, assuming userspace is paying any attention to the error return at all of course. We certainly have quite a lot of existing put() methods that do return errors and it's not like the application isn't invoking undefined behaviour so I don't see a problem here.

I find also it's more useful to have the proper checks in general.

Jaroslav, is you concern only about the compatibility of user-space? Or anything else? The compatibility is always certainly a slight issue; if this breaks really something useful and actually working stuff, we need to consider the workaround...

thanks,

Takashi

Jaroslav Kysela

maintainer

2022-01-24 19:21 UTC #7 lore raw

Quoted 21 lines · Takashi Iwai

Quoted 12 lines · Mark Brown
Quoted 9 lines · Jaroslav Kysela
Quoted 2 lines · Mark Brown
This series adds verification that values written to registers are in bounds for controls since the core doesn't validate for us.
As discussed, those conditions should be optional to eventually catch the wrong applications. I don't see any benefit to report the range error back when there is value masking code already. The users will note when the unwanted values are written to the hardware, or not?
Quoted 6 lines
In general I'd say that silent failures are harder to work with than returning an error at the point where we notice that there's a problem, assuming userspace is paying any attention to the error return at all of course. We certainly have quite a lot of existing put() methods that do return errors and it's not like the application isn't invoking undefined behaviour so I don't see a problem here.

Quoted 6 lines

I find also it's more useful to have the proper checks in general.
Jaroslav, is you concern only about the compatibility of user-space? Or anything else? The compatibility is always certainly a slight issue; if this breaks really something useful and actually working stuff, we need to consider the workaround...

My concern is only based on the fact that this code is normally not reachable. It only costs some CPU ticks and adds extra code to the drivers without any other benefit. The applications should not use out of range values and if they do, the behavior is not defined (the drivers should only avoid crashes).

The code seems to be added only to make things consistent for the test applications. I don't think that it's worth to care only for this reason. What is the goal for this code? The result with the proposed code will be - the SoC core has the extra validation conditions.

The user space can eventually add similar checks to detect the broken applications.

Basically, I think that those checks should be marked as debug and they should be optional like we do for CONFIG_SND_CTL_VALIDATION and enable only the fast path by default.

Jaroslav

Signature · 2 lines

Jaroslav Kysela <[email protected]>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

Mark Brown

author maintainer

2022-01-24 20:17 UTC #8 lore raw

Quoted 13 lines · Jaroslav Kysela

Quoted 4 lines · Takashi Iwai
Jaroslav, is you concern only about the compatibility of user-space? Or anything else? The compatibility is always certainly a slight issue; if this breaks really something useful and actually working stuff, we need to consider the workaround...
My concern is only based on the fact that this code is normally not reachable. It only costs some CPU ticks and adds extra code to the drivers without any other benefit. The applications should not use out of range values and if they do, the behavior is not defined (the drivers should only avoid crashes).

Quoted 4 lines

The code seems to be added only to make things consistent for the test applications. I don't think that it's worth to care only for this reason. What is the goal for this code? The result with the proposed code will be - the SoC core has the extra validation conditions.

We need these checks all the time for the generic ASoC controls since the values for the controls are stored in the underlying device's register map so the out of range values will be written to the hardware, pushing it out of specified use. That's not a great idea in general and in extreme cases could result in physical damage to the system. The biggest risk I see here is around speaker drivers since they deal with high powers, even ignoring silicon requirements we also don't currently enforce platform maximums that the machine drivers specify - that feature was added after an inexperienced user burnt out the speakers in their Chromebook since the speakers in the system were rated for much lower powers than the CODEC was able to deliver.

Quoted 3 lines

Basically, I think that those checks should be marked as debug and they should be optional like we do for CONFIG_SND_CTL_VALIDATION and enable only the fast path by default.

Note also that for everything using these helpers the underlying register map will be regmap based and with the possible exception of MMIO based regmaps the cost of writing out the new register value will be overwhelmingly greater than that of the bounds checks. It is extremely hard to envision a scenario in which even a pathological application would be able to observe a meaningful performance impact.

Jaroslav Kysela

maintainer

2022-01-24 20:53 UTC #9 lore raw

Quoted 19 lines · Mark Brown

Quoted 13 lines · Jaroslav Kysela
Quoted 4 lines · Takashi Iwai
Jaroslav, is you concern only about the compatibility of user-space? Or anything else? The compatibility is always certainly a slight issue; if this breaks really something useful and actually working stuff, we need to consider the workaround...
My concern is only based on the fact that this code is normally not reachable. It only costs some CPU ticks and adds extra code to the drivers without any other benefit. The applications should not use out of range values and if they do, the behavior is not defined (the drivers should only avoid crashes).
Quoted 4 lines
The code seems to be added only to make things consistent for the test applications. I don't think that it's worth to care only for this reason. What is the goal for this code? The result with the proposed code will be - the SoC core has the extra validation conditions.

Quoted 11 lines

We need these checks all the time for the generic ASoC controls since the values for the controls are stored in the underlying device's register map so the out of range values will be written to the hardware, pushing it out of specified use. That's not a great idea in general and in extreme cases could result in physical damage to the system. The biggest risk I see here is around speaker drivers since they deal with high powers, even ignoring silicon requirements we also don't currently enforce platform maximums that the machine drivers specify - that feature was added after an inexperienced user burnt out the speakers in their Chromebook since the speakers in the system were rated for much lower powers than the CODEC was able to deliver.

It may be good to add this to the comment for two related patches. It's not obvious from the first glance. So one condition is a must.

Quoted 10 lines

Quoted 3 lines
Basically, I think that those checks should be marked as debug and they should be optional like we do for CONFIG_SND_CTL_VALIDATION and enable only the fast path by default.
Note also that for everything using these helpers the underlying register map will be regmap based and with the possible exception of MMIO based regmaps the cost of writing out the new register value will be overwhelmingly greater than that of the bounds checks. It is extremely hard to envision a scenario in which even a pathological application would be able to observe a meaningful performance impact.

It's true that your patches are touching the universal code.

I stop complain for now. I just don't like to add chunks of the extra code just to resolve something which is not eventually a problem.

Jaroslav

Signature · 2 lines

Jaroslav Kysela <[email protected]>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

Mark Brown

author maintainer

2022-01-25 14:35 UTC #10 lore raw

In reply to Mark Brown

Quoted 9 lines · Mark Brown

This series adds verification that values written to registers are in bounds for controls since the core doesn't validate for us.
Mark Brown (3):
ASoC: ops: Reject out of bounds values in snd_soc_put_volsw()
ASoC: ops: Reject out of bounds values in snd_soc_put_volsw_sx()
ASoC: ops: Reject out of bounds values in snd_soc_put_xr_sx()
[...]

Applied to

https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-linus

Thanks!

[1/3] ASoC: ops: Reject out of bounds values in snd_soc_put_volsw()

      commit: 817f7c9335ec01e0f5e8caffc4f1dcd5e458a4c0
[2/3] ASoC: ops: Reject out of bounds values in snd_soc_put_volsw_sx()
      commit: 4f1e50d6a9cf9c1b8c859d449b5031cacfa8404e
[3/3] ASoC: ops: Reject out of bounds values in snd_soc_put_xr_sx()
      commit: 4cf28e9ae6e2e11a044be1bcbcfa1b0d8675fe4d

All being well this means that it will be integrated into the linux-next tree (usually sometime in the next 24 hours) and sent to Linus during the next merge window (or sooner if it is a bug fix), however if problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing and review of the tree, please engage with people reporting problems and send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they should be sent as incremental updates against current git, existing patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying to this mail.

Thanks,
Mark