This is a note to let you know that I've just added the patch titled x86/unwind/orc: Disable KASAN checking in the ORC unwinder, part 2 to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-unwind-orc-disable-kasan-checking-in-the-orc-unwinder-part-2.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From e504e74cc3a2c092b05577ce3e8e013fae7d94e6 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Date: Fri, 5 Feb 2021 08:24:02 -0600 Subject: x86/unwind/orc: Disable KASAN checking in the ORC unwinder, part 2 From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> commit e504e74cc3a2c092b05577ce3e8e013fae7d94e6 upstream. KASAN reserves "redzone" areas between stack frames in order to detect stack overruns. A read or write to such an area triggers a KASAN "stack-out-of-bounds" BUG. Normally, the ORC unwinder stays in-bounds and doesn't access the redzone. But sometimes it can't find ORC metadata for a given instruction. This can happen for code which is missing ORC metadata, or for generated code. In such cases, the unwinder attempts to fall back to frame pointers, as a best-effort type thing. This fallback often works, but when it doesn't, the unwinder can get confused and go off into the weeds into the KASAN redzone, triggering the aforementioned KASAN BUG. But in this case, the unwinder's confusion is actually harmless and working as designed. It already has checks in place to prevent off-stack accesses, but those checks get short-circuited by the KASAN BUG. And a BUG is a lot more disruptive than a harmless unwinder warning. Disable the KASAN checks by using READ_ONCE_NOCHECK() for all stack accesses. This finishes the job started by commit 881125bfe65b ("x86/unwind: Disable KASAN checking in the ORC unwinder"), which only partially fixed the issue. Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder") Reported-by: Ivan Babrou <ivan@xxxxxxxxxxxxxx> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Tested-by: Ivan Babrou <ivan@xxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxx Link: https://lkml.kernel.org/r/9583327904ebbbeda399eca9c56d6c7085ac20fe.1612534649.git.jpoimboe@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/unwind_orc.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) --- a/arch/x86/kernel/unwind_orc.c +++ b/arch/x86/kernel/unwind_orc.c @@ -367,8 +367,8 @@ static bool deref_stack_regs(struct unwi if (!stack_access_ok(state, addr, sizeof(struct pt_regs))) return false; - *ip = regs->ip; - *sp = regs->sp; + *ip = READ_ONCE_NOCHECK(regs->ip); + *sp = READ_ONCE_NOCHECK(regs->sp); return true; } @@ -380,8 +380,8 @@ static bool deref_stack_iret_regs(struct if (!stack_access_ok(state, addr, IRET_FRAME_SIZE)) return false; - *ip = regs->ip; - *sp = regs->sp; + *ip = READ_ONCE_NOCHECK(regs->ip); + *sp = READ_ONCE_NOCHECK(regs->sp); return true; } @@ -402,12 +402,12 @@ static bool get_reg(struct unwind_state return false; if (state->full_regs) { - *val = ((unsigned long *)state->regs)[reg]; + *val = READ_ONCE_NOCHECK(((unsigned long *)state->regs)[reg]); return true; } if (state->prev_regs) { - *val = ((unsigned long *)state->prev_regs)[reg]; + *val = READ_ONCE_NOCHECK(((unsigned long *)state->prev_regs)[reg]); return true; } Patches currently in stable-queue which might be from jpoimboe@xxxxxxxxxx are queue-5.10/x86-unwind-orc-disable-kasan-checking-in-the-orc-unwinder-part-2.patch