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Merge "NetlinkEvent: use isKernel64Bit in KernelUtils.h"

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Maciej Żenczykowski 2023-05-19 05:24:22 +00:00 committed by Gerrit Code Review
commit 97055b7ee9
2 changed files with 6 additions and 54 deletions
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4
libsysutils/Android.bp
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@ -29,6 +29,10 @@ cc_library {
"liblog",
],
header_libs: [
"bpf_headers",
],
export_include_dirs: ["include"],
tidy: true,

56
libsysutils/src/NetlinkEvent.cpp
View file

@ -37,10 +37,12 @@
#include <sys/utsname.h>
#include <android-base/parseint.h>
#include <bpf/KernelUtils.h>
#include <log/log.h>
#include <sysutils/NetlinkEvent.h>
using android::base::ParseInt;
using android::bpf::isKernel64Bit;
/* From kernel's net/netfilter/xt_quota2.c */
const int LOCAL_QLOG_NL_EVENT = 112;
@ -138,60 +140,6 @@ static_assert(sizeof(ulog_packet_msg_t) == sizeof(ulog_packet_msg32_t) ||
static_assert(sizeof(ulog_packet_msg32_t) == 168);
static_assert(sizeof(ulog_packet_msg64_t) == 192);
// Figure out the bitness of userspace.
// Trivial and known at compile time.
static bool isUserspace64bit(void) {
return sizeof(long) == 8;
}
// Figure out the bitness of the kernel.
static bool isKernel64Bit(void) {
// a 64-bit userspace requires a 64-bit kernel
if (isUserspace64bit()) return true;
static bool init = false;
static bool cache = false;
if (init) return cache;
// Retrieve current personality - on Linux this system call *cannot* fail.
int p = personality(0xffffffff);
// But if it does just assume kernel and userspace (which is 32-bit) match...
if (p == -1) return false;
// This will effectively mask out the bottom 8 bits, and switch to 'native'
// personality, and then return the previous personality of this thread
// (likely PER_LINUX or PER_LINUX32) with any extra options unmodified.
int q = personality((p & ~PER_MASK) | PER_LINUX);
// Per man page this theoretically could error out with EINVAL,
// but kernel code analysis suggests setting PER_LINUX cannot fail.
// Either way, assume kernel and userspace (which is 32-bit) match...
if (q != p) return false;
struct utsname u;
(void)uname(&u); // only possible failure is EFAULT, but u is on stack.
// Switch back to previous personality.
// Theoretically could fail with EINVAL on arm64 with no 32-bit support,
// but then we wouldn't have fetched 'p' from the kernel in the first place.
// Either way there's nothing meaningul we can do in case of error.
// Since PER_LINUX32 vs PER_LINUX only affects uname.machine it doesn't
// really hurt us either. We're really just switching back to be 'clean'.
(void)personality(p);
// Possible values of utsname.machine observed on x86_64 desktop (arm via qemu):
// x86_64 i686 aarch64 armv7l
// additionally observed on arm device:
// armv8l
// presumably also might just be possible:
// i386 i486 i586
// and there might be other weird arm32 cases.
// We note that the 64 is present in both 64-bit archs,
// and in general is likely to be present in only 64-bit archs.
cache = !!strstr(u.machine, "64");
init = true;
return cache;
}
/******************************************************************************/
NetlinkEvent::NetlinkEvent() {