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| author | Gregory Price <gourry.memverge@gmail.com> | 2023-04-07 13:18:32 -0400 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2023-04-16 14:23:07 +0200 |
| commit | 463b7715e7ce367fce89769c5d85e31595715ee1 (patch) | |
| tree | fd74da6fa4a4de6fc0c3e7d888ee221ce8f72948 /kernel/entry/syscall_user_dispatch.c | |
| parent | 43360686328b1f4b7d9dcc883ee9243ad7c16fae (diff) | |
| download | lwn-463b7715e7ce367fce89769c5d85e31595715ee1.tar.gz lwn-463b7715e7ce367fce89769c5d85e31595715ee1.zip | |
syscall_user_dispatch: Untag selector address before access_ok()
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
Diffstat (limited to 'kernel/entry/syscall_user_dispatch.c')
| -rw-r--r-- | kernel/entry/syscall_user_dispatch.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/kernel/entry/syscall_user_dispatch.c b/kernel/entry/syscall_user_dispatch.c index 22396b234854..7f2add43672d 100644 --- a/kernel/entry/syscall_user_dispatch.c +++ b/kernel/entry/syscall_user_dispatch.c @@ -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; |