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authorPeter Zijlstra <peterz@infradead.org>2023-07-19 23:15:38 +0300
committerPeter Zijlstra <peterz@infradead.org>2023-07-21 00:03:50 +0300
commit2e7e5bbb1c3c8d502edeb5c0670eac4995134b6f (patch)
tree49f390144bd21e3c987e15d85b3022584b5d2d7c /arch/x86
parentfdf0eaf11452d72945af31804e2a1048ee1b574c (diff)
downloadlinux-2e7e5bbb1c3c8d502edeb5c0670eac4995134b6f.tar.xz
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/x86')
-rw-r--r--arch/x86/entry/entry_64.S16
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