The following commit has been merged into the core/entry branch of tip: Commit-ID: 463b7715e7ce367fce89769c5d85e31595715ee1 Gitweb: https://git.kernel.org/tip/463b7715e7ce367fce89769c5d85e31595715ee1 Author: Gregory Price <gourry.memverge@xxxxxxxxx> AuthorDate: Fri, 07 Apr 2023 13:18:32 -04:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Sun, 16 Apr 2023 14:23:07 +02:00 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@xxxxxxx> Signed-off-by: Gregory Price <gregory.price@xxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx> Link: https://lore.kernel.org/all/ZCWXE04nLZ4pXEtM@xxxxxxx/ Link: https://lore.kernel.org/r/20230407171834.3558-3-gregory.price@xxxxxxxxxxxx --- kernel/entry/syscall_user_dispatch.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/entry/syscall_user_dispatch.c b/kernel/entry/syscall_user_dispatch.c index 22396b2..7f2add4 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;
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