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Add helper function for MADV_WIPEONFORK.

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BoringSSL (which is the crypto library used by most Google products) is starting to use madvise(_, _, MADV_WIPEONFORK) to protect random-number state from being duplicated by fork(). This causes extra madvise calls that sandboxes need to permit in order to continue functioning.

PiperOrigin-RevId: 309173849
Change-Id: I007dacc1ff1fd0ccc138caaa08735cfe5bc78234
This commit is contained in:
Sandboxed API Team 2020-04-30 00:08:31 -07:00 committed by Copybara-Service
parent fea5e8c485
commit 79049b09c0
2 changed files with 21 additions and 0 deletions
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15
sandboxed_api/sandbox2/policybuilder.cc
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@ -85,6 +85,7 @@ PolicyBuilder& PolicyBuilder::AllowScudoMalloc() {
AllowFutexOp(FUTEX_WAKE); AllowFutexOp(FUTEX_WAKE);
AllowLimitedMadvise(); AllowLimitedMadvise();
AllowGetRandom(); AllowGetRandom();
AllowWipeOnFork();
return AddPolicyOnMmap([](bpf_labels& labels) -> std::vector<sock_filter> { return AddPolicyOnMmap([](bpf_labels& labels) -> std::vector<sock_filter> {
return { return {
@ -426,6 +427,20 @@ PolicyBuilder& PolicyBuilder::AllowGetRandom() {
}); });
} }
PolicyBuilder& PolicyBuilder::AllowWipeOnFork() {
// System headers may not be recent enough to include MADV_WIPEONFORK.
static constexpr uint32_t kMadv_WipeOnFork = 18;
// The -1 value is used by code to probe that the kernel returns -EINVAL for
// unknown values because some environments, like qemu, ignore madvise
// completely, but code needs to know whether WIPEONFORK took effect.
return AddPolicyOnSyscall(__NR_madvise,
{
ARG_32(2),
JEQ32(kMadv_WipeOnFork, ALLOW),
JEQ32(static_cast<uint32_t>(-1), ALLOW),
});
}
PolicyBuilder& PolicyBuilder::AllowLogForwarding() { PolicyBuilder& PolicyBuilder::AllowLogForwarding() {
AllowWrite(); AllowWrite();
AllowSystemMalloc(); AllowSystemMalloc();

6
sandboxed_api/sandbox2/policybuilder.h
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@ -289,8 +289,14 @@ class PolicyBuilder final {
// Appends code to allow reading random bytes. // Appends code to allow reading random bytes.
// Allows these sycalls: // Allows these sycalls:
// - getrandom (with no flags or GRND_NONBLOCK) // - getrandom (with no flags or GRND_NONBLOCK)
//
PolicyBuilder& AllowGetRandom(); PolicyBuilder& AllowGetRandom();
// Appends code to allow configuring wipe-on-fork memory
// Allows these syscalls:
// - madvise (with advice equal to -1 or MADV_WIPEONFORK).
PolicyBuilder& AllowWipeOnFork();
// Enables syscalls required to use the logging support enabled via // Enables syscalls required to use the logging support enabled via
// Client::SendLogsToSupervisor() // Client::SendLogsToSupervisor()
// Allows the following: // Allows the following: