ACPR/android_system_core
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Enhance documentation about SetMmapRndBitsAction

Browse source 
Bug: N/A
Test: N/A
Change-Id: I0408158d181ef08831a55e1381477f5b128a5c52
This commit is contained in:
Jiyong Park 2022-07-18 09:17:39 +09:00
parent 11d7bc52df
commit 5b16ccb36e
1 changed files with 10 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
init/security.cpp
View file

@ -90,7 +90,7 @@ static bool SetMmapRndBitsMin(int start, int min, bool compat) {
// Set /proc/sys/vm/mmap_rnd_bits and potentially
// /proc/sys/vm/mmap_rnd_compat_bits to the maximum supported values.
// Returns -1 if unable to set these to an acceptable value.
// Returns an error if unable to set these to an acceptable value.
//
// To support this sysctl, the following upstream commits are needed:
//
@ -106,12 +106,19 @@ Result<void> SetMmapRndBitsAction(const BuiltinArguments&) {
// uml does not support mmap_rnd_bits
return {};
#elif defined(__aarch64__)
// arm64 supports 18 - 33 bits depending on pagesize and VA_SIZE
// arm64 architecture supports 18 - 33 rnd bits depending on pagesize and
// VA_SIZE. However the kernel might have been compiled with a narrower
// range using CONFIG_ARCH_MMAP_RND_BITS_MIN/MAX. To use the maximum
// supported number of bits, we start from the theoretical maximum of 33
// bits and try smaller values until we reach 24 bits which is the
// Android-specific minimum. Don't go lower even if the configured maximum
// is smaller than 24.
if (SetMmapRndBitsMin(33, 24, false) && (!Has32BitAbi() || SetMmapRndBitsMin(16, 16, true))) {
return {};
}
#elif defined(__x86_64__)
// x86_64 supports 28 - 32 bits
// x86_64 supports 28 - 32 rnd bits, but Android wants to ensure that the
// theoretical maximum of 32 bits is always supported and used.
if (SetMmapRndBitsMin(32, 32, false) && (!Has32BitAbi() || SetMmapRndBitsMin(16, 16, true))) {
return {};
}