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Kernel: Don't check pledges or veil against code coverage data files

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Coverage tools like LLVM's source-based coverage or GNU's --coverage
need to be able to write out coverage files from any binary, regardless
of its security posture. Not ignoring these pledges and veils means we
can't get our coverage data out without playing some serious tricks.

However this is pretty terrible for normal exeuction, so only skip these
checks when we explicitly configured userspace for coverage.
This commit is contained in:
Andrew Kaster 2022-03-04 18:05:24 -07:00 • committed by Andreas Kling
parent 5120b39d0e
commit f08e91f67e
3 changed files with 30 additions and 8 deletions
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4
Kernel/CMakeLists.txt
View file

@ -527,6 +527,10 @@ if (ENABLE_KERNEL_COVERAGE_COLLECTION)
../Kernel/Syscall.cpp
)
set_source_files_properties(${KCOV_EXCLUDED_SOURCES} PROPERTIES COMPILE_FLAGS "-fno-sanitize-coverage=trace-pc")
elseif (ENABLE_USERSPACE_COVERAGE_COLLECTION)
# Disable checking open() pledges and the veil for coverage data when building userspace with coverage
# so that binaries can write out coverage data even with pledges/veil
add_compile_definitions(SKIP_PATH_VALIDATION_FOR_COVERAGE_INSTRUMENTATION)
endif()
# Kernel Undefined Behavior Sanitizer (KUBSAN)

7
Kernel/FileSystem/VirtualFileSystem.cpp
View file

@ -771,6 +771,13 @@ ErrorOr<void> VirtualFileSystem::validate_path_against_process_veil(StringView p
VERIFY(!path.contains("/../"sv) && !path.ends_with("/.."sv));
VERIFY(!path.contains("/./"sv) && !path.ends_with("/."sv));
#ifdef SKIP_PATH_VALIDATION_FOR_COVERAGE_INSTRUMENTATION
// Skip veil validation against profile data when coverage is enabled for userspace
// so that all processes can write out coverage data even with veils in place
if (KLexicalPath::basename(path).ends_with(".profraw"sv))
return {};
#endif
auto& unveiled_path = find_matching_unveiled_path(path);
if (unveiled_path.permissions() == UnveilAccess::None) {
dbgln("Rejecting path '{}' since it hasn't been unveiled.", path);

15
Kernel/Syscalls/open.cpp
View file

@ -7,6 +7,7 @@
#include <Kernel/Debug.h>
#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/VirtualFileSystem.h>
#include <Kernel/KLexicalPath.h>
#include <Kernel/Net/LocalSocket.h>
#include <Kernel/Process.h>
@ -27,6 +28,17 @@ ErrorOr<FlatPtr> Process::sys$open(Userspace<Syscall::SC_open_params const*> use
if (options & O_UNLINK_INTERNAL)
return EINVAL;
auto path = TRY(get_syscall_path_argument(params.path));
// Disable checking open pledges when building userspace with coverage
// so that all processes can write out coverage data even with pledges
bool skip_pledge_verification = false;
#ifdef SKIP_PATH_VALIDATION_FOR_COVERAGE_INSTRUMENTATION
if (KLexicalPath::basename(path->view()).ends_with(".profraw"sv))
skip_pledge_verification = true;
#endif
if (!skip_pledge_verification) {
if (options & O_WRONLY)
TRY(require_promise(Pledge::wpath));
else if (options & O_RDONLY)
@ -34,12 +46,11 @@ ErrorOr<FlatPtr> Process::sys$open(Userspace<Syscall::SC_open_params const*> use
if (options & O_CREAT)
TRY(require_promise(Pledge::cpath));
}
// Ignore everything except permission bits.
mode &= 0777;
auto path = TRY(get_syscall_path_argument(params.path));
dbgln_if(IO_DEBUG, "sys$open(dirfd={}, path='{}', options={}, mode={})", dirfd, path->view(), options, mode);
auto fd_allocation = TRY(allocate_fd());