lib/posix-process: Add vfork & execve #1386

michpappas · 2024-04-16T16:08:05Z

Prerequisite checklist

Read the contribution guidelines regarding submitting new changes to the project;
Tested your changes against relevant architectures and platforms;
Ran the checkpatch.uk on your commit series before opening this PR;
Updated relevant documentation.

Base target

Architecture(s): [N/A]
Platform(s): [N/A]
Application(s): [N/A]

Additional configuration

CONFIG_LIBPOSIX_PROCESS_EXECVE: Enables the execve() syscall
CONFIG_LIBPOSIX_PROCESS_VFORK: Enables the vfork() syscall
CONFIG_LIBUKBINFMT: Enables the ukbinfmt library

Description of changes

This PR adds support for vfork() / execve() to libposix-process. This provides the foundation for running multiprocess applications on Unikraft.

vfork() creates a child process that shares the same memory with the calling thread, including the stack. Upon vfork() the parent is suspended until the child calls execve() or _exit() to prevent the parent's state from being corrupted. Due to above, the only permissible actions taken by the child are:

Update a variable of type pid_t to store its return value.
Calling any function other than one of the functions of the exec(2) family, or _exit(2).

Any action besides the above results into undefined behavior.

For a more elaborate description on vfork() see vfork(2).

execve() implements the standard behavior described in execve(2). To provide flexibility on the supported binary formats the implementation relies on libukbinfmt, which is also introducedin this series. Similarly to linux, this provides a minimal framework for registering loaders that handle different binary formats, introducing the ability of loading interpreted scripts. The implementation may be extended with support for linux's binfmt_misc fs, should such a use-case arise. The implementation of the ELF ukbinfmt loader is introduced in app-elfloader.

GitHub-Depends-On: #1316
GitHub-Depends-On: #1322
GitHub-Depends-On: #1346

libukbinfmt provides a minimal framework to register handlers of executable files. Typical examples include binary executables like ELF objects, or interpreted files like *nix scripts that use the sha-bang sequence to specify an interpreter. This commit only implements the functionality required to register and execute loaders within the kernel's scope. Additional functionality incl. application support via Linux's `binfmt_misc` API shall be added as a future extension. Checkpatch-Ignore: COMPLEX_MACRO Checkpatch-Ignore: MACRO_ARG_REUSE Signed-off-by: Michalis Pappas <michalis@unikraft.io>

Add definition of ARG_MAX to limits.h. POSIX defines ARG_MAX as the number of bytes available for the combined arguments and env vars of a new process. Whether that additionally includes NULL terminator, pointers, or alignment bytes is IMPLEMENTATION DEFINED. Signed-off-by: Michalis Pappas <michalis@unikraft.io>

Migrate the definitions of tid2pthread() and tid2pprocess() to the private process.h to make them available to the rest of the library. This requires to additionally migrate the definitions of struct posix_process() and struct posix_thread(). Signed-off-by: Michalis Pappas <michalis@unikraft.io>

The state provides information on whether a posix_thread is running, blocked, or exited. Notice that posix_thread_state is only updated by operations at the posix_process / posix_thread level and may not always be in sync with the state of the underlying uk_thread. This specifically applies to the POSIX_THREAD_RUNNING state, which may not be accurate e.g. if the underlying uk_thread blocks at the scheduler due to a lock. On the other hand, the variants of POSIX_STATE_BLOCKED always reflect the state of a posix_thread, as it is certain that the underlying uk_thread will also be blocked from the scheduler. Given the above, a check against POSIX_STATE_RUNNING should only be used to check if the state of a posix-thread is not terminated or blocked. Signed-off-by: Michalis Pappas <michalis@unikraft.io>

Add a field to posix_thread to keep track of its parent. This is populated during the creation of a posix_thread, and it is used for deriving the parent's state in execve() / exit(). Signed-off-by: Michalis Pappas <michalis@unikraft.io>

Add implementation for execve(). For more info see execve(2). Requires a binfmt ELF loader. The default loader is provided by app-bincompat. Checkpatch-Ignore: AVOID_EXTERNS Signed-off-by: Michalis Pappas <michalis@unikraft.io>

vfork() sets the CLONE_VM and CLONE_VFORK flags. This triggers an error in the clone handlers of vfscore as CLONE_FS is not set. Update the handlers to additionally check against CLONE_VM, as that also implies that the parent and child share filesystem state. Signed-off-by: Michalis Pappas <michalis@unikraft.io>

The vfork() syscall is equivalent to calling clone() with the flags parameter set to CLONE_VM | CLONE_VFORK | SIGCHLD. Update clone() to support CLONE_VFORK and CLONE_VM. Implement vfork() as a wrapper of clone(). For more info see vfork(2). Signed-off-by: Michalis Pappas <michalis@unikraft.io>

mogasergiu

Hi there 👋 👨‍⚕️ . Had a brief go at this. I will have a deeper look once we get the dependency PRs in.

mogasergiu · 2024-05-13T15:15:08Z

lib/Makefile.uk

@@ -70,3 +70,4 @@ $(eval $(call import_lib,$(CONFIG_UK_BASE)/lib/ukrust))
 $(eval $(call import_lib,$(CONFIG_UK_BASE)/lib/ukreloc))
 $(eval $(call import_lib,$(CONFIG_UK_BASE)/lib/ukofw))
 $(eval $(call import_lib,$(CONFIG_UK_BASE)/lib/ukallocstack))
+$(eval $(call import_lib,$(CONFIG_UK_BASE)/lib/ukbinfmt))


lib: Introduce libukbinfmt

s/sha-bang/shebang in the commit msg

mogasergiu · 2024-05-13T15:20:43Z

lib/ukbinfmt/include/uk/binfmt.h

@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+/* Copyright (c) 2023, Unikraft GmbH and The Unikraft Authors.


mogasergiu · 2024-05-13T15:23:32Z

lib/posix-process/process.h

@@ -58,6 +67,7 @@ struct posix_thread {
 	struct uk_list_head thread_list_entry;
 	struct uk_thread *thread;
 	struct uk_alloc *_a;
+	enum posix_thread_state state;


I would also add a comment here that states again the potential state difference between uk_thread and posix_thread

mogasergiu · 2024-05-13T15:24:31Z

lib/posix-process/arch/arm64/execve.c

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+/* Copyright (c) 2023, Unikraft GmbH and The Unikraft Authors.


mogasergiu · 2024-05-13T15:25:51Z

lib/posix-process/arch/x86_64/execve.c

+
+	/* Prepare for iret */
+	execenv->regs.eflags = X86_EFLAGS_IF; /* enable IRQs on ctx switch */
+	execenv->regs.cs = 8;


GDT_DESC_OFFSET(GDT_DESC_CODE) and GDT_DESC_OFFSET(GDT_DESC_DATA). yes this introduces deps to plat common 🤪

mogasergiu · 2024-05-13T15:42:30Z

lib/posix-process/arch/arm64/execve.c

+{
+	execenv->regs.lr = ip;
+	execenv->regs.sp = sp;
+


I think we should also set spsr_el1 as I believe it to have an unsafe value coming from a mallocd stack. I would reuse the one of the parent and, additionally &= ~PSR_I so that IRQs are enblaed. Ditto for x86, let's reuse the parents flags but with IRQs forcefully enabled (although I think in both cases it should be safe to assume they are already enabled IMO).

mogasergiu · 2024-05-13T15:46:59Z

lib/posix-process/arch/x86_64/execve.c

@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+/* Copyright (c) 2023, Unikraft GmbH and The Unikraft Authors.


2️⃣ 0️⃣ 2️⃣ 4️⃣

mogasergiu · 2024-05-13T15:48:00Z

lib/posix-process/clone.c

 *       still allocate an Unikraft TLS but sets the TLS architecture pointer
 *       to zero.
 */
-static int _clone(struct clone_args *cl_args, size_t cl_args_len,
-		  struct ukarch_execenv *execenv)
+int uk_clone(struct clone_args *cl_args, size_t cl_args_len,


mogasergiu · 2024-05-13T15:48:52Z

lib/posix-process/clone.c

+	if ((flags & CLONE_VM)) {
+		if (!cl_args->stack && !cl_args->stack_size) {
+			uk_pr_debug("Using parent's sp @ 0x%lx\n", execenv->regs.rsp);
+			cl_args->stack = execenv->regs.rsp; /* FIXME */


I assume FIXME cus x86 specific, right?

mogasergiu · 2024-05-13T15:50:24Z

lib/posix-process/clone.c

+	 * or exit(). Yield to schedule the child.
+	 */
+	if (flags & CLONE_VFORK) {
+		struct posix_thread *pthread = tid2pthread(ukthread2tid(t));


Subscope declaration? So unlike you 😞

michpappas requested review from a team as code owners April 16, 2024 16:08

michpappas mentioned this pull request Apr 16, 2024

Introduce ELF binfmt loader unikraft/app-elfloader#79

Open

nderjung added the release-note Denotes a PR that will be considered when it comes time to generate release notes. label Apr 16, 2024

mogasergiu and others added 10 commits April 26, 2024 09:17

PR unikraft#1316

854555a

PR unikraft#1346

1e4fd09

lib/posix-process: Add posix_thread parent

22a9ff0

Add a field to posix_thread to keep track of its parent. This is populated during the creation of a posix_thread, and it is used for deriving the parent's state in execve() / exit(). Signed-off-by: Michalis Pappas <michalis@unikraft.io>

lib/posix-process: Add execve()

348df61

Add implementation for execve(). For more info see execve(2). Requires a binfmt ELF loader. The default loader is provided by app-bincompat. Checkpatch-Ignore: AVOID_EXTERNS Signed-off-by: Michalis Pappas <michalis@unikraft.io>

michpappas force-pushed the michpappas/feature/vfork_execve branch from e2182e2 to 0ec4fed Compare April 26, 2024 07:20

github-actions bot added the area/support Support scripts, tools, services. label Apr 26, 2024

razvand requested a review from andreittr April 28, 2024 05:35

razvand assigned skuenzer Apr 28, 2024

razvand requested review from StefanJum, mariasfiraiala and RaduNichita and removed request for a team April 28, 2024 05:35

razvand added this to the v0.17.0 (Calypso) milestone Apr 28, 2024

mogasergiu requested changes May 13, 2024

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lib/posix-process: Add vfork & execve #1386

lib/posix-process: Add vfork & execve #1386

michpappas commented Apr 16, 2024

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		@@ -0,0 +1,102 @@
		/* SPDX-License-Identifier: BSD-3-Clause */
		/* Copyright (c) 2023, Unikraft GmbH and The Unikraft Authors.

		@@ -0,0 +1,20 @@
		/* SPDX-License-Identifier: BSD-3-Clause */
		/* Copyright (c) 2023, Unikraft GmbH and The Unikraft Authors.

		@@ -0,0 +1,29 @@
		/* SPDX-License-Identifier: BSD-3-Clause */
		/* Copyright (c) 2023, Unikraft GmbH and The Unikraft Authors.

lib/posix-process: Add vfork & execve #1386

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michpappas commented Apr 16, 2024

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