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syscall_user_dispatch: Add PR_SYS_DISPATCH_INCLUSIVE_ON

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There are two possible scenarios for syscall filtering:
 - having a trusted/allowed range of PCs, and intercepting everything else
 - or the opposite: a single untrusted/intercepted range and allowing
   everything else (this is relevant for any kind of sandboxing scenario,
   or monitoring behavior of a single library)

The current API only allows the former use case due to allowed
range wrap-around check. Add PR_SYS_DISPATCH_INCLUSIVE_ON that
enables the second use case.

Add PR_SYS_DISPATCH_EXCLUSIVE_ON alias for PR_SYS_DISPATCH_ON
to make it clear how it's different from the new
PR_SYS_DISPATCH_INCLUSIVE_ON.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/97947cc8e205ff49675826d7b0327ef2e2c66eea.1747839857.git.dvyukov@google.com
This commit is contained in:
Dmitry Vyukov
2025-05-21 17:04:29 +02:00
committed by Thomas Gleixner
parent b89732c8c8
commit a2fc422ed7
4 changed files with 48 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

36
kernel/entry/syscall_user_dispatch.c
View File

@@ -78,7 +78,7 @@ static int task_set_syscall_user_dispatch(struct task_struct *task, unsigned lon
if (offset || len || selector)
return -EINVAL;
break;
case PR_SYS_DISPATCH_ON:
case PR_SYS_DISPATCH_EXCLUSIVE_ON:
/*
* Validate the direct dispatcher region just for basic
* sanity against overflow and a 0-sized dispatcher
@@ -87,30 +87,40 @@ static int task_set_syscall_user_dispatch(struct task_struct *task, unsigned lon
*/
if (offset && offset + len <= offset)
return -EINVAL;
break;
case PR_SYS_DISPATCH_INCLUSIVE_ON:
if (len == 0 || offset + len <= offset)
return -EINVAL;
/*
* 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.
* Invert the range, the check in syscall_user_dispatch()
* supports wrap-around.
*/
if (selector && !access_ok(untagged_addr(selector), sizeof(*selector)))
return -EFAULT;
offset = offset + len;
len = -len;
break;
default:
return -EINVAL;
}
/*
* 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 (mode != PR_SYS_DISPATCH_OFF && selector &&
!access_ok(untagged_addr(selector), sizeof(*selector)))
return -EFAULT;
task->syscall_dispatch.selector = selector;
task->syscall_dispatch.offset = offset;
task->syscall_dispatch.len = len;
task->syscall_dispatch.on_dispatch = false;
if (mode == PR_SYS_DISPATCH_ON)
if (mode != PR_SYS_DISPATCH_OFF)
set_task_syscall_work(task, SYSCALL_USER_DISPATCH);
else
clear_task_syscall_work(task, SYSCALL_USER_DISPATCH);