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Kernel: Add a 'no_error' pledge promise

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This makes pledge() ignore promises that would otherwise cause it to
fail with EPERM, which is very useful for allowing programs to run under
a "jail" so to speak, without having them termiate early due to a
failing pledge() call.
This commit is contained in:
Ali Mohammad Pur 2022-03-25 01:17:42 +04:30 committed by Ali Mohammad Pur
parent 37073437c1
commit 8233da3398
Notes: sideshowbarker 2024-07-17 16:43:49 +09:00 
Author: https://github.com/alimpfard
Commit: https://github.com/SerenityOS/serenity/commit/8233da3398
Pull-request: https://github.com/SerenityOS/serenity/pull/13212
3 changed files with 12 additions and 5 deletions
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1
Base/usr/share/man/man2/pledge.md
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@ -54,6 +54,7 @@ If the process later attempts to use any system functionality it has previously
* `ptrace`: The [`ptrace`(2)](help://man/2/ptrace) syscall (\*)
* `prot_exec`: [`mmap`(2)](help://man/2/mmap) and [`mprotect`(2)](help://man/2/mprotect) with `PROT_EXEC`
* `map_fixed`: [`mmap`(2)](help://man/2/mmap) with `MAP_FIXED` or `MAP_FIXED_NOREPLACE` (\*)
* `no_error`: Ignore requests of pledge elevation going forwards, this is useful for enforcing _execpromises_ while the child process wants to ask for more upfront (Note that the elevation requests are _not_ granted, merely ignored), this is similar to the `error` pledge in OpenBSD.
Promises marked with an asterisk (\*) are SerenityOS specific extensions not supported by the original OpenBSD `pledge()`.

3
Kernel/Process.h
View file

@ -67,7 +67,8 @@ Time kgettimeofday();
__ENUMERATE_PLEDGE_PROMISE(setkeymap) \
__ENUMERATE_PLEDGE_PROMISE(prot_exec) \
__ENUMERATE_PLEDGE_PROMISE(map_fixed) \
__ENUMERATE_PLEDGE_PROMISE(getkeymap)
__ENUMERATE_PLEDGE_PROMISE(getkeymap) \
__ENUMERATE_PLEDGE_PROMISE(no_error)
enum class Pledge : u32 {
#define __ENUMERATE_PLEDGE_PROMISE(x) x,

5
Kernel/Syscalls/pledge.cpp
View file

@ -46,17 +46,22 @@ ErrorOr<FlatPtr> Process::sys$pledge(Userspace<const Syscall::SC_pledge_params*>
if (promises) {
if (!parse_pledge(promises->view(), new_promises))
return EINVAL;
if (!(m_protected_values.promises & (1u << (u32)Pledge::no_error))) {
if (m_protected_values.has_promises && (new_promises & ~m_protected_values.promises))
return EPERM;
}
}
u32 new_execpromises = 0;
if (execpromises) {
if (!parse_pledge(execpromises->view(), new_execpromises))
return EINVAL;
if (!(m_protected_values.promises & (1u << (u32)Pledge::no_error))) {
if (m_protected_values.has_execpromises && (new_execpromises & ~m_protected_values.execpromises))
return EPERM;
}
}
// Only apply promises after all validation has occurred, this ensures
// we don't introduce logic bugs like applying the promises, and then