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+From 417382aecd6964f97a0a0774a5cccd29c1b9edb3 Mon Sep 17 00:00:00 2001
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+From: Julien Olivain <ju.o@free.fr>
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+Date: Sat, 23 Sep 2023 13:09:23 +0200
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+Subject: [PATCH] kexec: provide a memfd_create() wrapper if not present in
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+ libc
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+
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+Commit 714fa115 "kexec/arm64: Simplify the code for zImage" introduced
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+a use of the memfd_create() system call, included in version
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+kexec-tools v2.0.27.
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+
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+This system call was introduced in kernel commit [1], first included
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+in kernel v3.17 (released on 2014-10-05).
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+
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+The memfd_create() glibc wrapper function was added much later in
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+commit [2], first included in glibc version 2.27 (released on
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+2018-02-01).
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+
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+This direct use memfd_create() introduced a requirement on
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+Kernel >= 3.17 and glibc >= 2.27.
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+
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+There is old toolchains like [3] for example (which ships gcc 7.3.1,
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+glibc 2.25 and includes kernel v4.10 headers), that can still be used
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+to build newer kernels. Even if such toolchains can be seen as
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+outdated, they are is still claimed as supported by recent kernel.
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+For example, Kernel v6.5.5 has a requirement on gcc version 5.1 and
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+greater. See [4].
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+
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+Moreover, kexec-tools <= 2.0.26 could be compiled using recent
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+toolchains with alternative libc (e.g. uclibc-ng, musl) which are not
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+providing the memfd_create() wrapper.
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+
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+When compiling kexec-tools v2.0.27 with a toolchain not providing the
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+memfd_create() syscall wrapper, the compilation fail with message:
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+
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+ kexec/kexec.c: In function 'copybuf_memfd':
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+ kexec/kexec.c:645:7: warning: implicit declaration of function 'memfd_create'; did you mean 'SYS_memfd_create'? [-Wimplicit-function-declaration]
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+ fd = memfd_create("kernel", MFD_ALLOW_SEALING);
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+ ^~~~~~~~~~~~
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+ SYS_memfd_create
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+ kexec/kexec.c:645:30: error: 'MFD_ALLOW_SEALING' undeclared (first use in this function); did you mean '_PC_ALLOC_SIZE_MIN'?
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+ fd = memfd_create("kernel", MFD_ALLOW_SEALING);
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+ ^~~~~~~~~~~~~~~~~
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+ _PC_ALLOC_SIZE_MIN
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+
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+In order to let kexec-tools compile in a wider range of configurations,
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+this commit adds a memfd_create() function check in autoconf configure
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+script, and adds a system call wrapper which will be used if the
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+function is not available. With this commit, the environment
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+requirement is relaxed to only kernel >= v3.17.
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+
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+Note: this issue was found in kexec-tools integration in Buildroot [5]
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+using the command "utils/test-pkg -a -p kexec", which tests many
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+toolchain/arch combinations.
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+
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+[1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9183df25fe7b194563db3fec6dc3202a5855839c
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+[2] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=59d2cbb1fe4b8601d5cbd359c3806973eab6c62d
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+[3] https://releases.linaro.org/components/toolchain/binaries/7.3-2018.05/aarch64-linux-gnu/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu.tar.xz
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+[4] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation/process/changes.rst?h=v6.5.5#n32
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+[5] https://buildroot.org/
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+
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+Upstream: https://lists.infradead.org/pipermail/kexec/2023-September/028168.html
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+Signed-off-by: Julien Olivain <ju.o@free.fr>
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+---
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+ configure.ac | 3 +++
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+ kexec/kexec.c | 11 +++++++++++
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+ 2 files changed, 14 insertions(+)
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+
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+diff --git a/configure.ac b/configure.ac
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+index 192976c..212ef2c 100644
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+--- a/configure.ac
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++++ b/configure.ac
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+@@ -208,6 +208,9 @@ if test "$ac_cv_lib_xenctrl_xc_kexec_load" = yes ; then
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+ AC_MSG_NOTICE([The kexec_status call is not available]))
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+ fi
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+
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++dnl Check if libc has the memfd_create() syscall wrapper
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++AC_CHECK_FUNCS([memfd_create])
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++
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+ dnl ---Sanity checks
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+ if test "$CC" = "no"; then AC_MSG_ERROR([cc not found]); fi
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+ if test "$CPP" = "no"; then AC_MSG_ERROR([cpp not found]); fi
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+diff --git a/kexec/kexec.c b/kexec/kexec.c
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+index c3b182e..c44c4b7 100644
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+--- a/kexec/kexec.c
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++++ b/kexec/kexec.c
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+@@ -31,6 +31,10 @@
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+ #include <sys/mount.h>
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+ #include <sys/types.h>
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+ #include <sys/stat.h>
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++#ifndef HAVE_MEMFD_CREATE
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++#include <linux/memfd.h>
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++#include <sys/syscall.h>
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++#endif
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+ #include <sys/reboot.h>
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+ #include <sys/mman.h>
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+ #include <unistd.h>
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+@@ -638,6 +642,13 @@ char *slurp_decompress_file(const char *filename, off_t *r_size)
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+ return kernel_buf;
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+ }
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+
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++#ifndef HAVE_MEMFD_CREATE
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++static int memfd_create(const char *name, unsigned int flags)
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++{
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++ return syscall(SYS_memfd_create, name, flags);
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++}
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++#endif
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++
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+ static int copybuf_memfd(const char *kernel_buf, size_t size)
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+ {
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+ int fd, count;
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+--
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+2.41.0
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+
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Julien Olivain