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syscall_user_dispatch: Untag selector address before access_ok()

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To support checkpoint/restart, ptrace must be able to set the selector
of the tracee.  The selector is a user pointer that may be subject to
memory tagging extensions on some architectures (namely ARM MTE).

access_ok() clears memory tags for tagged addresses if the current task has
memory tagging enabled.

This obviously fails when ptrace modifies the selector of a tracee when
tracer and tracee do not have the same memory tagging enabled state.

Solve this by untagging the selector address before handing it to
access_ok(), like other ptrace functions which modify tracee pointers do.

Obviously a tracer can set an invalid selector address for the tracee, but
that's independent of tagging and a general capability of the tracer.

Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/all/ZCWXE04nLZ4pXEtM@arm.com/
Link: https://lore.kernel.org/r/20230407171834.3558-3-gregory.price@memverge.com
This commit is contained in:
Gregory Price 2023-04-07 13:18:32 -04:00 committed by Thomas Gleixner
parent 4336068632
commit 463b7715e7
1 changed files with 10 additions and 1 deletions
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11
kernel/entry/syscall_user_dispatch.c
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@ -87,7 +87,16 @@ static int task_set_syscall_user_dispatch(struct task_struct *task, unsigned lon
if (offset && offset + len <= offset)
return -EINVAL;
if (selector && !access_ok(selector, sizeof(*selector)))
/*
* access_ok() will clear memory tags for tagged addresses
* if current has memory tagging enabled.
* To enable a tracer to set a tracees selector the
* selector address must be untagged for access_ok(),
* otherwise an untagged tracer will always fail to set a
* tagged tracees selector.
*/
if (selector && !access_ok(untagged_addr(selector), sizeof(*selector)))
return -EFAULT;
break;