Dear Greg,
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
Best Regards Michał Mirosław
On Sun, Mar 07, 2021 at 04:00:40PM +0100, Michał Mirosław wrote:
Dear Greg,
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
Looks like a new feature to me, right?
How many patches, and have you tested them? If so, submit them as a patch series and we can review them, but if this is a new feature, it does not meet the stable kernel rules.
And why not just use 5.11 or newer for discovering kernel bugs? Why does 5.10 matter here?
thanks,
greg k-h
(+ Russell)
On Sun, 7 Mar 2021 at 16:21, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
On Sun, Mar 07, 2021 at 04:00:40PM +0100, Michał Mirosław wrote:
Dear Greg,
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
Looks like a new feature to me, right?
How many patches, and have you tested them? If so, submit them as a patch series and we can review them, but if this is a new feature, it does not meet the stable kernel rules.
And why not just use 5.11 or newer for discovering kernel bugs? Why does 5.10 matter here?
The KASan support was rather tricky to get right, so I don't think this is suitable for stable. The range 7a1be318f579..421015713b30 is definitely not complete (we'd need at least e9a2f8b599d0bc22a1b13e69527246ac39c697b4 and 10fce53c0ef8f6e79115c3d9e0d7ea1338c3fa37 as well), and the intrusive nature of those changes means they are definitely not appropriate as stable backports.
On Sun, Mar 07, 2021 at 05:10:43PM +0100, Ard Biesheuvel wrote:
(+ Russell)
On Sun, 7 Mar 2021 at 16:21, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
On Sun, Mar 07, 2021 at 04:00:40PM +0100, Michał Mirosław wrote:
Dear Greg,
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
Looks like a new feature to me, right?
How many patches, and have you tested them? If so, submit them as a patch series and we can review them, but if this is a new feature, it does not meet the stable kernel rules.
And why not just use 5.11 or newer for discovering kernel bugs? Why does 5.10 matter here?
The KASan support was rather tricky to get right, so I don't think this is suitable for stable. The range 7a1be318f579..421015713b30 is definitely not complete (we'd need at least e9a2f8b599d0bc22a1b13e69527246ac39c697b4 and 10fce53c0ef8f6e79115c3d9e0d7ea1338c3fa37 as well), and the intrusive nature of those changes means they are definitely not appropriate as stable backports.
I agree - it took quite a while for KASan to settle down - and our last issue with KASan causing a panic in the Kprobes codes was in February. So, I think at the very least, requesting to backport this so soon is premature. That fix is not included even in what you mention above. Maybe that fix has already been picked up in stable, I don't know.
So, we know that there's probably more to getting kprobes working on 32-bit ARM than even you've mentioned above.
Is it worth backporting such a major feature to stable kernels? Or would it be better to backport the fixes found by KASan from later kernels? My feeling is the latter is the better all round approach.
On Sun, Mar 07, 2021 at 10:48:54PM +0000, Russell King - ARM Linux admin wrote:
On Sun, Mar 07, 2021 at 05:10:43PM +0100, Ard Biesheuvel wrote:
(+ Russell)
On Sun, 7 Mar 2021 at 16:21, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
On Sun, Mar 07, 2021 at 04:00:40PM +0100, Michał Mirosław wrote:
Dear Greg,
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
Looks like a new feature to me, right?
How many patches, and have you tested them? If so, submit them as a patch series and we can review them, but if this is a new feature, it does not meet the stable kernel rules.
And why not just use 5.11 or newer for discovering kernel bugs? Why does 5.10 matter here?
The KASan support was rather tricky to get right, so I don't think this is suitable for stable. The range 7a1be318f579..421015713b30 is definitely not complete (we'd need at least e9a2f8b599d0bc22a1b13e69527246ac39c697b4 and 10fce53c0ef8f6e79115c3d9e0d7ea1338c3fa37 as well), and the intrusive nature of those changes means they are definitely not appropriate as stable backports.
I agree - it took quite a while for KASan to settle down - and our last issue with KASan causing a panic in the Kprobes codes was in February. So, I think at the very least, requesting to backport this so soon is premature. That fix is not included even in what you mention above. Maybe that fix has already been picked up in stable, I don't know.
So, we know that there's probably more to getting kprobes working on 32-bit ARM than even you've mentioned above.
Is it worth backporting such a major feature to stable kernels? Or would it be better to backport the fixes found by KASan from later kernels? My feeling is the latter is the better all round approach.
I guessed that KASan support code does not pose problems with CONFIG_KASAN=n. If it does, then I understand that this is definitely a deal-breaker for stable, and I agree there is no point in further discussion. But, if in disabled state KASan patches meet the stable requirements, then maybe it is worth the trouble to help those who have to stay on a LTS kernel?
Regarding testing KASan for ARM: I'm currently running it on a SAMA5D2 board. The 4 patches on top of v5.10.21 did allow the device to boot up (after fixing a false-positive in __clear_user_memset()). I also applied the three patches Ard mentioned just to be closer to upstream and the board still went up. Kernel gets big and slow after enabling KASan, but I think this is expected.
Best Regards Michał Mirosław
On Mon, Mar 08, 2021 at 12:34:39AM +0100, Michał Mirosław wrote:
On Sun, Mar 07, 2021 at 10:48:54PM +0000, Russell King - ARM Linux admin wrote:
On Sun, Mar 07, 2021 at 05:10:43PM +0100, Ard Biesheuvel wrote:
(+ Russell)
On Sun, 7 Mar 2021 at 16:21, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
On Sun, Mar 07, 2021 at 04:00:40PM +0100, Michał Mirosław wrote:
Dear Greg,
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
Looks like a new feature to me, right?
How many patches, and have you tested them? If so, submit them as a patch series and we can review them, but if this is a new feature, it does not meet the stable kernel rules.
And why not just use 5.11 or newer for discovering kernel bugs? Why does 5.10 matter here?
The KASan support was rather tricky to get right, so I don't think this is suitable for stable. The range 7a1be318f579..421015713b30 is definitely not complete (we'd need at least e9a2f8b599d0bc22a1b13e69527246ac39c697b4 and 10fce53c0ef8f6e79115c3d9e0d7ea1338c3fa37 as well), and the intrusive nature of those changes means they are definitely not appropriate as stable backports.
I agree - it took quite a while for KASan to settle down - and our last issue with KASan causing a panic in the Kprobes codes was in February. So, I think at the very least, requesting to backport this so soon is premature. That fix is not included even in what you mention above. Maybe that fix has already been picked up in stable, I don't know.
So, we know that there's probably more to getting kprobes working on 32-bit ARM than even you've mentioned above.
Is it worth backporting such a major feature to stable kernels? Or would it be better to backport the fixes found by KASan from later kernels? My feeling is the latter is the better all round approach.
I guessed that KASan support code does not pose problems with CONFIG_KASAN=n. If it does, then I understand that this is definitely a deal-breaker for stable, and I agree there is no point in further discussion. But, if in disabled state KASan patches meet the stable requirements, then maybe it is worth the trouble to help those who have to stay on a LTS kernel?
Following this logic nearly every upstream feature can be backported to stable.
You can't have both worlds; you can't stay on an older "stable" tree while still benefiting from new features that land upstream.
On Mon, Mar 08, 2021 at 12:34:39AM +0100, Michał Mirosław wrote:
On Sun, Mar 07, 2021 at 10:48:54PM +0000, Russell King - ARM Linux admin wrote:
On Sun, Mar 07, 2021 at 05:10:43PM +0100, Ard Biesheuvel wrote:
(+ Russell)
On Sun, 7 Mar 2021 at 16:21, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
On Sun, Mar 07, 2021 at 04:00:40PM +0100, Michał Mirosław wrote:
Dear Greg,
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
Looks like a new feature to me, right?
How many patches, and have you tested them? If so, submit them as a patch series and we can review them, but if this is a new feature, it does not meet the stable kernel rules.
And why not just use 5.11 or newer for discovering kernel bugs? Why does 5.10 matter here?
The KASan support was rather tricky to get right, so I don't think this is suitable for stable. The range 7a1be318f579..421015713b30 is definitely not complete (we'd need at least e9a2f8b599d0bc22a1b13e69527246ac39c697b4 and 10fce53c0ef8f6e79115c3d9e0d7ea1338c3fa37 as well), and the intrusive nature of those changes means they are definitely not appropriate as stable backports.
I agree - it took quite a while for KASan to settle down - and our last issue with KASan causing a panic in the Kprobes codes was in February. So, I think at the very least, requesting to backport this so soon is premature. That fix is not included even in what you mention above. Maybe that fix has already been picked up in stable, I don't know.
So, we know that there's probably more to getting kprobes working on 32-bit ARM than even you've mentioned above.
Is it worth backporting such a major feature to stable kernels? Or would it be better to backport the fixes found by KASan from later kernels? My feeling is the latter is the better all round approach.
I guessed that KASan support code does not pose problems with CONFIG_KASAN=n. If it does, then I understand that this is definitely a deal-breaker for stable, and I agree there is no point in further discussion. But, if in disabled state KASan patches meet the stable requirements, then maybe it is worth the trouble to help those who have to stay on a LTS kernel?
Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for what types of patches are acceptable for stable kernels. These do not seem to fit into those categories at all.
thanks,
greg k-h
On Sun, Mar 7, 2021 at 4:00 PM Michał Mirosław mirq-linux@rere.qmqm.pl wrote:
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
It's a development feature not supposed to be enabled in production/product kernels and following the stable kernel rules I don't see what this code would achieve in stable.
IMO it's a better idea to provide a branch with KASan for each stable branch that developers can pull in if they want to enable it and use it for testing.
Are you interested in setting up such branches for others to use? I think it would be helpful. Also the work shouldn't be very hard after bring-up and it ends when the last stable pre-v5.11 kernel is EOL:ed.
Yours, Linus Walleij
On Mon, Mar 08, 2021 at 10:44:03AM +0100, Linus Walleij wrote:
On Sun, Mar 7, 2021 at 4:00 PM Michał Mirosław mirq-linux@rere.qmqm.pl wrote:
Would you consider KASan for ARM patches for LTS (5.10) kernel? Those are 7a1be318f579..421015713b30 if I understand correctly. They are not normal stable material, but I think they will help tremendously in discovering kernel bugs on 32-bit ARMs.
It's a development feature not supposed to be enabled in production/product kernels and following the stable kernel rules I don't see what this code would achieve in stable.
IMO it's a better idea to provide a branch with KASan for each stable branch that developers can pull in if they want to enable it and use it for testing.
Are you interested in setting up such branches for others to use? I think it would be helpful. Also the work shouldn't be very hard after bring-up and it ends when the last stable pre-v5.11 kernel is EOL:ed.
This is just a few patches, so I've posted the branch at my git repo. Please clone after fetching stable/linux-5.10.x from kernel.org:
git remote add rere git://rere.qmqm.pl/linux git fetch rere refs/heads/kasan-for-arm-510
Best Regards, Michał Mirosław
linux-stable-mirror@lists.linaro.org
-
Ard Biesheuvel -
Greg Kroah-Hartman -
Linus Walleij -
Michał Mirosław -
Michał Mirosław
-
Russell King - ARM Linux admin -
Sasha Levin