git: 2a519c3b14c2 - main - kasan: Disable validation of function parameters passed by value

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=2a519c3b14c29688e42d11f916655318b13c8409

commit 2a519c3b14c29688e42d11f916655318b13c8409
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2021-11-03 16:28:48 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2021-11-03 16:36:02 +0000

    kasan: Disable validation of function parameters passed by value
    
    It appears that the emitted code in the caller does not update shadow
    state for values passed on the stack to the callee, which it seemingly
    ought to do after pushing values on the stack and prior to the call
    itself.  This leaves open a window where an interrupt handler can cause
    regions of the stack containing these values to be poisoned, resulting
    in rare false positive reports.  This happens particularly in the amd64
    TLB invalidation code, where we liberally pass cpuset_t's around by
    value.
    
    LLVM has a flag to disable validation of accesses of function parameters
    passed by value.  Such validation is itself a relatively new feature.
    Turn it off for now.
    
    Reported by:    pho, syzkaller
    MFC after:      2 weeks
    Sponsored by:   The FreeBSD Foundation
---
 sys/conf/kern.pre.mk | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/conf/kern.pre.mk b/sys/conf/kern.pre.mk
index 9d9e32027ec7..056963adcb2d 100644
--- a/sys/conf/kern.pre.mk
+++ b/sys/conf/kern.pre.mk
@@ -100,7 +100,8 @@ SAN_CFLAGS+=	-DSAN_NEEDS_INTERCEPTORS -DSAN_INTERCEPTOR_PREFIX=kasan \
 		-mllvm -asan-instrument-dynamic-allocas=true \
 		-mllvm -asan-globals=true \
 		-mllvm -asan-use-after-scope=true \
-		-mllvm -asan-instrumentation-with-call-threshold=0
+		-mllvm -asan-instrumentation-with-call-threshold=0 \
+		-mllvm -asan-instrument-byval=false
 .endif
 
 KCSAN_ENABLED!=	grep KCSAN opt_global.h || true ; echo