diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2023-07-19 22:15:38 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-07-20 23:03:50 +0200 |
| commit | 2e7e5bbb1c3c8d502edeb5c0670eac4995134b6f (patch) | |
| tree | 49f390144bd21e3c987e15d85b3022584b5d2d7c /arch | |
| parent | fdf0eaf11452d72945af31804e2a1048ee1b574c (diff) | |
x86: Fix kthread unwind
The rewrite of ret_from_form() misplaced an unwind hint which caused
all kthread stack unwinds to be marked unreliable, breaking
livepatching.
Restore the annotation and add a comment to explain the how and why of
things.
Fixes: 3aec4ecb3d1f ("x86: Rewrite ret_from_fork() in C")
Reported-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Petr Mladek <pmladek@suse.com>
Link: https://lkml.kernel.org/r/20230719201538.GA3553016@hirez.programming.kicks-ass.net
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/entry/entry_64.S | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 91f6818884fa..43606de22511 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -285,7 +285,15 @@ SYM_FUNC_END(__switch_to_asm) */ .pushsection .text, "ax" SYM_CODE_START(ret_from_fork_asm) - UNWIND_HINT_REGS + /* + * This is the start of the kernel stack; even through there's a + * register set at the top, the regset isn't necessarily coherent + * (consider kthreads) and one cannot unwind further. + * + * This ensures stack unwinds of kernel threads terminate in a known + * good state. + */ + UNWIND_HINT_END_OF_STACK ANNOTATE_NOENDBR // copy_thread CALL_DEPTH_ACCOUNT @@ -295,6 +303,12 @@ SYM_CODE_START(ret_from_fork_asm) movq %r12, %rcx /* fn_arg */ call ret_from_fork + /* + * Set the stack state to what is expected for the target function + * -- at this point the register set should be a valid user set + * and unwind should work normally. + */ + UNWIND_HINT_REGS jmp swapgs_restore_regs_and_return_to_usermode SYM_CODE_END(ret_from_fork_asm) .popsection |