[PATCH 1/2] host/rootfs: remove /proc/kcore bind mounts

[PATCH 1/2] host/rootfs: remove /proc/kcore bind mounts

[Alyssa Ross]

Neither of these services run as root any more, so they don't have
access to /proc/kcore any more regardless.  (Also we don't have
/proc/kcore on aarch64 so this previously errored there.)

Fixes: 62590b8 ("host/rootfs: Sandbox crosvm")
Fixes: ec47d36 ("host/rootfs: Sandbox Cloud Hypervisor")
Signed-off-by: Alyssa Ross <hi@alyssa.is>
---
 .../service/vm-services/template/data/service/vhost-user-gpu/run | 1 -
 host/rootfs/image/usr/bin/run-vmm                                | 1 -
 2 files changed, 2 deletions(-)

diff --git a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
index b1f9bac..e063a82 100755
--- a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
+++ b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
@@ -40,7 +40,6 @@ bwrap
   --tmpfs /proc/irq
   --remount-ro /proc/irq
   --ro-bind /dev/null /proc/timer_list
-  --ro-bind /dev/null /proc/kcore
   --ro-bind /dev/null /proc/kallsyms
   --ro-bind /dev/null /proc/sysrq-trigger
   --
diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
index 0640239..e30b14c 100755
--- a/host/rootfs/image/usr/bin/run-vmm
+++ b/host/rootfs/image/usr/bin/run-vmm
@@ -113,7 +113,6 @@ bwrap
   --tmpfs /proc/irq
   --remount-ro /proc/irq
   --ro-bind /dev/null /proc/timer_list
-  --ro-bind /dev/null /proc/kcore
   --ro-bind /dev/null /proc/kallsyms
   --ro-bind /dev/null /proc/sysrq-trigger
   --

base-commit: 6ceeb9b236cc50d2bba90068533ca1b7ff229c8b
-- 
2.51.0

[PATCH 2/2] host/rootfs: disable CONFIG_PROC_SCSI in kernel

[Alyssa Ross]

This is a legacy interface.  I doubt anything in Spectrum depends on
it.  The previous approach of masking it out with Bubblewrap failed on
aarch64, where it was already disabled in the kernel config.

Fixes: 62590b8 ("host/rootfs: Sandbox crosvm")
Fixes: ec47d36 ("host/rootfs: Sandbox Cloud Hypervisor")
Signed-off-by: Alyssa Ross <hi@alyssa.is>
---
This also means the floodgates are now open for any other rootfs kernel 
changes that anybody wants to propose.

 host/rootfs/default.nix                                     | 6 +++++-
 .../vm-services/template/data/service/vhost-user-gpu/run    | 2 --
 host/rootfs/image/usr/bin/run-vmm                           | 2 --
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/host/rootfs/default.nix b/host/rootfs/default.nix
index 66aa366..26757ef 100644
--- a/host/rootfs/default.nix
+++ b/host/rootfs/default.nix
@@ -49,7 +49,11 @@ let
     system.stateVersion = trivial.release;
   });
 
-  kernel = linux_latest;
+  kernel = linux_latest.override {
+    structuredExtraConfig = with lib.kernel; {
+      SCSI_PROC_FS = no;
+    };
+  };
 
   appvm = callSpectrumPackage ../../img/app { inherit (foot) terminfo; };
   netvm = callSpectrumPackage ../../vm/sys/net { inherit (foot) terminfo; };
diff --git a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
index e063a82..bdd842e 100755
--- a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
+++ b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
@@ -31,8 +31,6 @@ bwrap
   --disable-userns
   --proc /proc
   --ro-bind /proc/sys /proc/sys
-  --tmpfs /proc/scsi
-  --remount-ro /proc/scsi
   --tmpfs /proc/acpi
   --remount-ro /proc/acpi
   --tmpfs /proc/fs
diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
index e30b14c..d71f7eb 100755
--- a/host/rootfs/image/usr/bin/run-vmm
+++ b/host/rootfs/image/usr/bin/run-vmm
@@ -104,8 +104,6 @@ bwrap
   --bind /run /run
   --proc /proc
   --ro-bind /proc/sys /proc/sys
-  --tmpfs /proc/scsi
-  --remount-ro /proc/scsi
   --tmpfs /proc/acpi
   --remount-ro /proc/acpi
   --tmpfs /proc/fs
-- 
2.51.0

Re: [PATCH 2/2] host/rootfs: disable CONFIG_PROC_SCSI in kernel

[Demi Marie Obenour]

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On 12/15/25 07:27, Alyssa Ross wrote:
> This is a legacy interface.  I doubt anything in Spectrum depends on
> it.  The previous approach of masking it out with Bubblewrap failed on
> aarch64, where it was already disabled in the kernel config.
> 
> Fixes: 62590b8 ("host/rootfs: Sandbox crosvm")
> Fixes: ec47d36 ("host/rootfs: Sandbox Cloud Hypervisor")
> Signed-off-by: Alyssa Ross <hi@alyssa.is>
> ---
> This also means the floodgates are now open for any other rootfs kernel 
> changes that anybody wants to propose.

I'll start by disabling non-AF_UNIX, non-AF_NETLINK networking!

>  host/rootfs/default.nix                                     | 6 +++++-
>  .../vm-services/template/data/service/vhost-user-gpu/run    | 2 --
>  host/rootfs/image/usr/bin/run-vmm                           | 2 --
>  3 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/host/rootfs/default.nix b/host/rootfs/default.nix
> index 66aa366..26757ef 100644
> --- a/host/rootfs/default.nix
> +++ b/host/rootfs/default.nix
> @@ -49,7 +49,11 @@ let
>      system.stateVersion = trivial.release;
>    });
>  
> -  kernel = linux_latest;
> +  kernel = linux_latest.override {
> +    structuredExtraConfig = with lib.kernel; {
> +      SCSI_PROC_FS = no;
> +    };
> +  };
>  
>    appvm = callSpectrumPackage ../../img/app { inherit (foot) terminfo; };
>    netvm = callSpectrumPackage ../../vm/sys/net { inherit (foot) terminfo; };
> diff --git a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
> index e063a82..bdd842e 100755
> --- a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
> +++ b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
> @@ -31,8 +31,6 @@ bwrap
>    --disable-userns
>    --proc /proc
>    --ro-bind /proc/sys /proc/sys
> -  --tmpfs /proc/scsi
> -  --remount-ro /proc/scsi
>    --tmpfs /proc/acpi
>    --remount-ro /proc/acpi
>    --tmpfs /proc/fs
> diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
> index e30b14c..d71f7eb 100755
> --- a/host/rootfs/image/usr/bin/run-vmm
> +++ b/host/rootfs/image/usr/bin/run-vmm
> @@ -104,8 +104,6 @@ bwrap
>    --bind /run /run
>    --proc /proc
>    --ro-bind /proc/sys /proc/sys
> -  --tmpfs /proc/scsi
> -  --remount-ro /proc/scsi
>    --tmpfs /proc/acpi
>    --remount-ro /proc/acpi
>    --tmpfs /proc/fs

Acked-by: Demi Marie Obenour <demiobenour@gmail.com>
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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Re: [PATCH 1/2] host/rootfs: remove /proc/kcore bind mounts

[Demi Marie Obenour]

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On 12/15/25 07:27, Alyssa Ross wrote:
> Neither of these services run as root any more, so they don't have
> access to /proc/kcore any more regardless.  (Also we don't have
> /proc/kcore on aarch64 so this previously errored there.)
> 
> Fixes: 62590b8 ("host/rootfs: Sandbox crosvm")
> Fixes: ec47d36 ("host/rootfs: Sandbox Cloud Hypervisor")
> Signed-off-by: Alyssa Ross <hi@alyssa.is>
> ---
>  .../service/vm-services/template/data/service/vhost-user-gpu/run | 1 -
>  host/rootfs/image/usr/bin/run-vmm                                | 1 -
>  2 files changed, 2 deletions(-)
> 
> diff --git a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
> index b1f9bac..e063a82 100755
> --- a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
> +++ b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
> @@ -40,7 +40,6 @@ bwrap
>    --tmpfs /proc/irq
>    --remount-ro /proc/irq
>    --ro-bind /dev/null /proc/timer_list
> -  --ro-bind /dev/null /proc/kcore
>    --ro-bind /dev/null /proc/kallsyms
>    --ro-bind /dev/null /proc/sysrq-trigger
>    --
> diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
> index 0640239..e30b14c 100755
> --- a/host/rootfs/image/usr/bin/run-vmm
> +++ b/host/rootfs/image/usr/bin/run-vmm
> @@ -113,7 +113,6 @@ bwrap
>    --tmpfs /proc/irq
>    --remount-ro /proc/irq
>    --ro-bind /dev/null /proc/timer_list
> -  --ro-bind /dev/null /proc/kcore
>    --ro-bind /dev/null /proc/kallsyms
>    --ro-bind /dev/null /proc/sysrq-trigger
>    --
> 
> base-commit: 6ceeb9b236cc50d2bba90068533ca1b7ff229c8b

/proc/sysrq-trigger and /proc/timer_list can also be dropped,
as they are not accessible to unprivileged users.

With or without that change:

Reviewed-by: Demi Marie Obenour <demiobenour@gmail.com>
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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Re: [PATCH 1/2] host/rootfs: remove /proc/kcore bind mounts

[Alyssa Ross]

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Demi Marie Obenour <demiobenour@gmail.com> writes:

> On 12/15/25 07:27, Alyssa Ross wrote:
>> Neither of these services run as root any more, so they don't have
>> access to /proc/kcore any more regardless.  (Also we don't have
>> /proc/kcore on aarch64 so this previously errored there.)
>> 
>> Fixes: 62590b8 ("host/rootfs: Sandbox crosvm")
>> Fixes: ec47d36 ("host/rootfs: Sandbox Cloud Hypervisor")
>> Signed-off-by: Alyssa Ross <hi@alyssa.is>
>> ---
>>  .../service/vm-services/template/data/service/vhost-user-gpu/run | 1 -
>>  host/rootfs/image/usr/bin/run-vmm                                | 1 -
>>  2 files changed, 2 deletions(-)
>> 
>> diff --git a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>> index b1f9bac..e063a82 100755
>> --- a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>> +++ b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>> @@ -40,7 +40,6 @@ bwrap
>>    --tmpfs /proc/irq
>>    --remount-ro /proc/irq
>>    --ro-bind /dev/null /proc/timer_list
>> -  --ro-bind /dev/null /proc/kcore
>>    --ro-bind /dev/null /proc/kallsyms
>>    --ro-bind /dev/null /proc/sysrq-trigger
>>    --
>> diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
>> index 0640239..e30b14c 100755
>> --- a/host/rootfs/image/usr/bin/run-vmm
>> +++ b/host/rootfs/image/usr/bin/run-vmm
>> @@ -113,7 +113,6 @@ bwrap
>>    --tmpfs /proc/irq
>>    --remount-ro /proc/irq
>>    --ro-bind /dev/null /proc/timer_list
>> -  --ro-bind /dev/null /proc/kcore
>>    --ro-bind /dev/null /proc/kallsyms
>>    --ro-bind /dev/null /proc/sysrq-trigger
>>    --
>> 
>> base-commit: 6ceeb9b236cc50d2bba90068533ca1b7ff229c8b
>
> /proc/sysrq-trigger and /proc/timer_list can also be dropped,
> as they are not accessible to unprivileged users.

And what about the others?  I see systemd just makes them all read-only
— is that only to protect against root?  Do we still need to hide
/proc/sys, /proc/scsi, /proc/acpi, /proc/fs, and /proc/irq?  The only
entry I see that's writable by non-root in any of those on my NixOS
system is /proc/sys/kernel/ns_last_pid, which doesn't look very harmful…

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Re: [PATCH 1/2] host/rootfs: remove /proc/kcore bind mounts

[Alyssa Ross]

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Alyssa Ross <hi@alyssa.is> writes:

> Demi Marie Obenour <demiobenour@gmail.com> writes:
>
>> On 12/15/25 07:27, Alyssa Ross wrote:
>>> Neither of these services run as root any more, so they don't have
>>> access to /proc/kcore any more regardless.  (Also we don't have
>>> /proc/kcore on aarch64 so this previously errored there.)
>>> 
>>> Fixes: 62590b8 ("host/rootfs: Sandbox crosvm")
>>> Fixes: ec47d36 ("host/rootfs: Sandbox Cloud Hypervisor")
>>> Signed-off-by: Alyssa Ross <hi@alyssa.is>
>>> ---
>>>  .../service/vm-services/template/data/service/vhost-user-gpu/run | 1 -
>>>  host/rootfs/image/usr/bin/run-vmm                                | 1 -
>>>  2 files changed, 2 deletions(-)
>>> 
>>> diff --git a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>> index b1f9bac..e063a82 100755
>>> --- a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>> +++ b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>> @@ -40,7 +40,6 @@ bwrap
>>>    --tmpfs /proc/irq
>>>    --remount-ro /proc/irq
>>>    --ro-bind /dev/null /proc/timer_list
>>> -  --ro-bind /dev/null /proc/kcore
>>>    --ro-bind /dev/null /proc/kallsyms
>>>    --ro-bind /dev/null /proc/sysrq-trigger
>>>    --
>>> diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
>>> index 0640239..e30b14c 100755
>>> --- a/host/rootfs/image/usr/bin/run-vmm
>>> +++ b/host/rootfs/image/usr/bin/run-vmm
>>> @@ -113,7 +113,6 @@ bwrap
>>>    --tmpfs /proc/irq
>>>    --remount-ro /proc/irq
>>>    --ro-bind /dev/null /proc/timer_list
>>> -  --ro-bind /dev/null /proc/kcore
>>>    --ro-bind /dev/null /proc/kallsyms
>>>    --ro-bind /dev/null /proc/sysrq-trigger
>>>    --
>>> 
>>> base-commit: 6ceeb9b236cc50d2bba90068533ca1b7ff229c8b
>>
>> /proc/sysrq-trigger and /proc/timer_list can also be dropped,
>> as they are not accessible to unprivileged users.
>
> And what about the others?  I see systemd just makes them all read-only
> — is that only to protect against root?  Do we still need to hide
> /proc/sys, /proc/scsi, /proc/acpi, /proc/fs, and /proc/irq?  The only
> entry I see that's writable by non-root in any of those on my NixOS
> system is /proc/sys/kernel/ns_last_pid, which doesn't look very harmful…

I'm just going to drop the /proc/scsi bind mount as well for now to fix
aarch64, but if you still think it's necessary we can instead do the
kernel config change.

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Re: [PATCH 1/2] host/rootfs: remove /proc/kcore bind mounts

[Alyssa Ross]

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Alyssa Ross <hi@alyssa.is> writes:

> Alyssa Ross <hi@alyssa.is> writes:
>
>> Demi Marie Obenour <demiobenour@gmail.com> writes:
>>
>>> On 12/15/25 07:27, Alyssa Ross wrote:
>>>> Neither of these services run as root any more, so they don't have
>>>> access to /proc/kcore any more regardless.  (Also we don't have
>>>> /proc/kcore on aarch64 so this previously errored there.)
>>>> 
>>>> Fixes: 62590b8 ("host/rootfs: Sandbox crosvm")
>>>> Fixes: ec47d36 ("host/rootfs: Sandbox Cloud Hypervisor")
>>>> Signed-off-by: Alyssa Ross <hi@alyssa.is>
>>>> ---
>>>>  .../service/vm-services/template/data/service/vhost-user-gpu/run | 1 -
>>>>  host/rootfs/image/usr/bin/run-vmm                                | 1 -
>>>>  2 files changed, 2 deletions(-)
>>>> 
>>>> diff --git a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>>> index b1f9bac..e063a82 100755
>>>> --- a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>>> +++ b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>>> @@ -40,7 +40,6 @@ bwrap
>>>>    --tmpfs /proc/irq
>>>>    --remount-ro /proc/irq
>>>>    --ro-bind /dev/null /proc/timer_list
>>>> -  --ro-bind /dev/null /proc/kcore
>>>>    --ro-bind /dev/null /proc/kallsyms
>>>>    --ro-bind /dev/null /proc/sysrq-trigger
>>>>    --
>>>> diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
>>>> index 0640239..e30b14c 100755
>>>> --- a/host/rootfs/image/usr/bin/run-vmm
>>>> +++ b/host/rootfs/image/usr/bin/run-vmm
>>>> @@ -113,7 +113,6 @@ bwrap
>>>>    --tmpfs /proc/irq
>>>>    --remount-ro /proc/irq
>>>>    --ro-bind /dev/null /proc/timer_list
>>>> -  --ro-bind /dev/null /proc/kcore
>>>>    --ro-bind /dev/null /proc/kallsyms
>>>>    --ro-bind /dev/null /proc/sysrq-trigger
>>>>    --
>>>> 
>>>> base-commit: 6ceeb9b236cc50d2bba90068533ca1b7ff229c8b
>>>
>>> /proc/sysrq-trigger and /proc/timer_list can also be dropped,
>>> as they are not accessible to unprivileged users.
>>
>> And what about the others?  I see systemd just makes them all read-only
>> — is that only to protect against root?  Do we still need to hide
>> /proc/sys, /proc/scsi, /proc/acpi, /proc/fs, and /proc/irq?  The only
>> entry I see that's writable by non-root in any of those on my NixOS
>> system is /proc/sys/kernel/ns_last_pid, which doesn't look very harmful…
>
> I'm just going to drop the /proc/scsi bind mount as well for now to fix
> aarch64, but if you still think it's necessary we can instead do the
> kernel config change.

(and same with /proc/acpi, now done)

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Re: [PATCH 1/2] host/rootfs: remove /proc/kcore bind mounts

[Demi Marie Obenour]

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On 12/16/25 04:55, Alyssa Ross wrote:
> Demi Marie Obenour <demiobenour@gmail.com> writes:
> 
>> On 12/15/25 07:27, Alyssa Ross wrote:
>>> Neither of these services run as root any more, so they don't have
>>> access to /proc/kcore any more regardless.  (Also we don't have
>>> /proc/kcore on aarch64 so this previously errored there.)
>>>
>>> Fixes: 62590b8 ("host/rootfs: Sandbox crosvm")
>>> Fixes: ec47d36 ("host/rootfs: Sandbox Cloud Hypervisor")
>>> Signed-off-by: Alyssa Ross <hi@alyssa.is>
>>> ---
>>>  .../service/vm-services/template/data/service/vhost-user-gpu/run | 1 -
>>>  host/rootfs/image/usr/bin/run-vmm                                | 1 -
>>>  2 files changed, 2 deletions(-)
>>>
>>> diff --git a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>> index b1f9bac..e063a82 100755
>>> --- a/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>> +++ b/host/rootfs/image/etc/s6-linux-init/run-image/service/vm-services/template/data/service/vhost-user-gpu/run
>>> @@ -40,7 +40,6 @@ bwrap
>>>    --tmpfs /proc/irq
>>>    --remount-ro /proc/irq
>>>    --ro-bind /dev/null /proc/timer_list
>>> -  --ro-bind /dev/null /proc/kcore
>>>    --ro-bind /dev/null /proc/kallsyms
>>>    --ro-bind /dev/null /proc/sysrq-trigger
>>>    --
>>> diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
>>> index 0640239..e30b14c 100755
>>> --- a/host/rootfs/image/usr/bin/run-vmm
>>> +++ b/host/rootfs/image/usr/bin/run-vmm
>>> @@ -113,7 +113,6 @@ bwrap
>>>    --tmpfs /proc/irq
>>>    --remount-ro /proc/irq
>>>    --ro-bind /dev/null /proc/timer_list
>>> -  --ro-bind /dev/null /proc/kcore
>>>    --ro-bind /dev/null /proc/kallsyms
>>>    --ro-bind /dev/null /proc/sysrq-trigger
>>>    --
>>>
>>> base-commit: 6ceeb9b236cc50d2bba90068533ca1b7ff229c8b
>>
>> /proc/sysrq-trigger and /proc/timer_list can also be dropped,
>> as they are not accessible to unprivileged users.
> 
> And what about the others?  I see systemd just makes them all read-only
> — is that only to protect against root?  Do we still need to hide
> /proc/sys, /proc/scsi, /proc/acpi, /proc/fs, and /proc/irq?  The only
> entry I see that's writable by non-root in any of those on my NixOS
> system is /proc/sys/kernel/ns_last_pid, which doesn't look very harmful…

I think it is indeed to protect against root.  In particular, some
container runtimes try to maintain a security boundary even when
user namespaces are not in use.  /proc/sys/kernel/ns_last_pid is
indeed harmless.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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Re: [PATCH 1/2] host/rootfs: remove /proc/kcore bind mounts

[Alyssa Ross]

This patch has been committed as 8dfd042c2cf64f53cfd39a24697a20e585ad1b6c,
which can be viewed online at
https://spectrum-os.org/git/spectrum/commit/?id=8dfd042c2cf64f53cfd39a24697a20e585ad1b6c.

This is an automated message.  Send comments/questions/requests to:
Alyssa Ross <hi@alyssa.is>