Hi!
From: Josh Poimboeuf jpoimboe@redhat.com
commit 98d0c8ebf77e0ba7c54a9ae05ea588f0e9e3f46e upstream.
If the unwinder is called before the ORC data has been initialized, orc_find() returns NULL, and it tries to fall back to using frame pointers. This can cause some unexpected warnings during boot.
Move the 'orc_init' check from orc_find() to __unwind_init(), so that it doesn't even try to unwind from an uninitialized state.
@@ -563,6 +560,9 @@ EXPORT_SYMBOL_GPL(unwind_next_frame); void __unwind_start(struct unwind_state *state, struct task_struct *task, struct pt_regs *regs, unsigned long *first_frame) {
- if (!orc_init)
goto done;- memset(state, 0, sizeof(*state)); state->task = task;
As this returns the *state to the caller, should the "goto done" move below the memset? Otherwise we are returning partialy-initialized struct, which is ... weird.
Yeah, it is a little weird. In most cases it should be fine, but there is an edge case where if there's a corrupt ORC table and this returns early, 'arch_stack_walk_reliable() -> unwind_error()' could check an uninitialized value.
Also the __unwind_start() error handling needs to set that error bit anyway, in its error cases. I'll fix it up.
I did this in the mean time. It moves goto around memset, and I believe that 8 in get_reg should have been sizeof(long) [not that it matters, x86-32 is protected by build bug on.]
Signed-off-by: Pavel Machek pavel@ucw.cz
Best regards, Pavel
diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c index 169b96492b7c..90cb3cb2b4f1 100644 --- a/arch/x86/kernel/unwind_orc.c +++ b/arch/x86/kernel/unwind_orc.c @@ -375,7 +375,7 @@ static bool deref_stack_iret_regs(struct unwind_state *state, unsigned long addr static bool get_reg(struct unwind_state *state, unsigned int reg_off, unsigned long *val) { - unsigned int reg = reg_off/8; + unsigned int reg = reg_off/sizeof(long);
if (!state->regs) return false; @@ -589,12 +589,12 @@ EXPORT_SYMBOL_GPL(unwind_next_frame); void __unwind_start(struct unwind_state *state, struct task_struct *task, struct pt_regs *regs, unsigned long *first_frame) { - if (!orc_init) - goto done; - memset(state, 0, sizeof(*state)); state->task = task;
+ if (!orc_init) + goto done; + /* * Refuse to unwind the stack of a task while it's executing on another * CPU. This check is racy, but that's ok: the unwinder has other