From 8a117a374bd71dc21a42f5a4bdbe3324ca5357d8 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= Date: Fri, 16 Jun 2023 08:18:49 +0000 Subject: [PATCH] bpfLoader: automatically bump ringbuffer size up to page size MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit A 4kB BPF_MAP_TYPE_RINGBUF does not work on 16kB page size kernel, as an eBPF ring buffer size *must* be a multiple of the page size. However, it is inefficient to force a 16kB RINGBUF on kernels with only a 4kB page size. It wastes 12kB of mlock'ed memory per ring buffer, which isn't much, but - as we add more ringbuffers - it'll add up... The userspace ring buffer code doesn't actually mind the automatic increase in size, as it retrieves the actual size from the map fd (ie. from the kernel) during init and thus adjusts automatically. Test: TreeHugger Bug: 279819914 Signed-off-by: Maciej Żenczykowski Change-Id: I9fcb1f9dc2e86038a7f1a486f4efbc28dba38ca0 --- libbpf_android/Loader.cpp | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/libbpf_android/Loader.cpp b/libbpf_android/Loader.cpp index 71a5a64..231fe39 100644 --- a/libbpf_android/Loader.cpp +++ b/libbpf_android/Loader.cpp @@ -31,13 +31,13 @@ #include #include -// This is BpfLoader v0.39 +// This is BpfLoader v0.40 // WARNING: If you ever hit cherrypick conflicts here you're doing it wrong: // You are NOT allowed to cherrypick bpfloader related patches out of order. // (indeed: cherrypicking is probably a bad idea and you should merge instead) // Mainline supports ONLY the published versions of the bpfloader for each Android release. #define BPFLOADER_VERSION_MAJOR 0u -#define BPFLOADER_VERSION_MINOR 39u +#define BPFLOADER_VERSION_MINOR 40u #define BPFLOADER_VERSION ((BPFLOADER_VERSION_MAJOR << 16) | BPFLOADER_VERSION_MINOR) #include "BpfSyscallWrappers.h" @@ -95,6 +95,8 @@ const std::string& getBuildType() { return t; } +static unsigned int page_size = static_cast(getpagesize()); + constexpr const char* lookupSelinuxContext(const domain d, const char* const unspecified = "") { switch (d) { case domain::unspecified: return unspecified; @@ -705,6 +707,11 @@ static bool mapMatchesExpectations(const unique_fd& fd, const string& mapName, if (type == BPF_MAP_TYPE_DEVMAP || type == BPF_MAP_TYPE_DEVMAP_HASH) desired_map_flags |= BPF_F_RDONLY_PROG; + unsigned int desired_max_entries = mapDef.max_entries; + if (type == BPF_MAP_TYPE_RINGBUF) { + if (desired_max_entries < page_size) desired_max_entries = page_size; + } + // The following checks should *never* trigger, if one of them somehow does, // it probably means a bpf .o file has been changed/replaced at runtime // and bpfloader was manually rerun (normally it should only run *once* @@ -715,7 +722,7 @@ static bool mapMatchesExpectations(const unique_fd& fd, const string& mapName, if ((fd_type == type) && (fd_key_size == (int)mapDef.key_size) && (fd_value_size == (int)mapDef.value_size) && - (fd_max_entries == (int)mapDef.max_entries) && + (fd_max_entries == (int)desired_max_entries) && (fd_map_flags == desired_map_flags)) { return true; } @@ -842,6 +849,11 @@ static int createMaps(const char* elfPath, ifstream& elfFile, vector& type = BPF_MAP_TYPE_HASH; } + unsigned int max_entries = md[i].max_entries; + if (type == BPF_MAP_TYPE_RINGBUF) { + if (max_entries < page_size) max_entries = page_size; + } + domain selinux_context = getDomainFromSelinuxContext(md[i].selinux_context); if (specified(selinux_context)) { if (!inDomainBitmask(selinux_context, allowedDomainBitmask)) { @@ -887,7 +899,7 @@ static int createMaps(const char* elfPath, ifstream& elfFile, vector& .map_flags = md[i].map_flags, .key_size = md[i].key_size, .value_size = md[i].value_size, - .max_entries = md[i].max_entries, + .max_entries = max_entries, }; if (btfFd.has_value() && btfTypeIdMap.find(mapNames[i]) != btfTypeIdMap.end()) { attr.btf_fd = btfFd->get();