From: Jeff Xu <jeffxu@xxxxxxxxxx> Add documentation for sysctl vm.memfd_noexec Link:https://lore.kernel.org/linux-mm/CABi2SkXUX_QqTQ10Yx9bBUGpN1wByOi_=gZU6WEy5a8MaQY3Jw@xxxxxxxxxxxxxx/T/ Reported-by: Dominique Martinet <asmadeus@xxxxxxxxxxxxx> Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxx> --- Documentation/admin-guide/sysctl/vm.rst | 30 +++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index 45ba1f4dc004..621588041a9e 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -424,6 +424,36 @@ e.g., up to one or two maps per allocation. The default value is 65530. +memfd_noexec: +============= +This pid namespaced sysctl controls memfd_create(). + +The new MFD_NOEXEC_SEAL and MFD_EXEC flags of memfd_create() allows +application to set executable bit at creation time. + +When MFD_NOEXEC_SEAL is set, memfd is created without executable bit +(mode:0666), and sealed with F_SEAL_EXEC, so it can't be chmod to +be executable (mode: 0777) after creation. + +when MFD_EXEC flag is set, memfd is created with executable bit +(mode:0777), this is the same as the old behavior of memfd_create. + +The new pid namespaced sysctl vm.memfd_noexec has 3 values: +0: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL acts like + MFD_EXEC was set. +1: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL acts like + MFD_NOEXEC_SEAL was set. +2: memfd_create() without MFD_NOEXEC_SEAL will be rejected. + +The default value is 0. + +Once set, it can't be downgraded at runtime, i.e. 2=>1, 1=>0 +are denied. + +This is pid namespaced sysctl, child processes inherit the parent +process's memfd_noexec at the time of fork. Changes to the parent +process after fork are not automatically propagated to the child +process. memory_failure_early_kill: ========================== -- 2.41.0.255.g8b1d071c50-goog
