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Subject[rfc linux-next 3/3] [RFC] prctl: prctl_set_mm -- Bring back handling of PR_SET_MM_x
Recently the handling of PR_SET_MM_x been removed because we wanted to
improve locking scheme over mm::arg_start,arg_end and etc. Thus to
reduce code modification the old PR_SET_MM_x operations have been
removed (since initially they've been introduced for c/r sole sake).
Before making remove I googled if there are some users of this interface
exist and happened to miss that at least systemd is already using
PR_SET_MM_ARG_START and PR_SET_MM_ARG_END (see src/basic/process-util.c)

Also Jonathan pointed me that there is a need for sole PR_SET_MM_x
operations.

https://lkml.org/lkml/2018/5/6/127

Here is a trick: since prctl_set_mm_map now accepts struct prctl_mm_map
as an argument we can fetch current mm settings, modify the member requested
and send the map into prctl_set_mm_map directly, which simply gonna be
like an emulation of PR_SET_MM_MAP. Thus users of PR_SET_MM_x should
be able to continue utilizing the interface.

CC: Jonathan de Boyne Pollard <J.deBoynePollard-newsgroups@NTLWorld.COM>
CC: Andrey Vagin <avagin@openvz.org>
CC: Andrew Morton <akpm@linuxfoundation.org>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
CC: Yang Shi <yang.shi@linux.alibaba.com>
CC: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
---
kernel/sys.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 57 insertions(+), 8 deletions(-)

Index: linux-ml.git/kernel/sys.c
===================================================================
--- linux-ml.git.orig/kernel/sys.c
+++ linux-ml.git/kernel/sys.c
@@ -1815,7 +1815,6 @@ SYSCALL_DEFINE1(umask, int, mask)
return mask;
}

-#ifdef CONFIG_CHECKPOINT_RESTORE
/*
* WARNING: we don't require any capability here so be very careful
* in what is allowed for modification from userspace.
@@ -2046,19 +2045,36 @@ static int prctl_set_mm_map(struct prctl
up_read(&mm->mmap_sem);
return 0;
}
-#endif /* CONFIG_CHECKPOINT_RESTORE */

static int prctl_set_mm(int opt, unsigned long addr,
unsigned long arg4, unsigned long arg5)
{
-#ifdef CONFIG_CHECKPOINT_RESTORE
+ static const unsigned char offsets[] = {
+ [PR_SET_MM_START_CODE] = offsetof(struct prctl_mm_map, start_code),
+ [PR_SET_MM_END_CODE] = offsetof(struct prctl_mm_map, end_code),
+ [PR_SET_MM_START_DATA] = offsetof(struct prctl_mm_map, start_data),
+ [PR_SET_MM_END_DATA] = offsetof(struct prctl_mm_map, end_data),
+ [PR_SET_MM_START_STACK] = offsetof(struct prctl_mm_map, start_brk),
+ [PR_SET_MM_START_BRK] = offsetof(struct prctl_mm_map, brk),
+ [PR_SET_MM_BRK] = offsetof(struct prctl_mm_map, start_stack),
+ [PR_SET_MM_ARG_START] = offsetof(struct prctl_mm_map, arg_start),
+ [PR_SET_MM_ARG_END] = offsetof(struct prctl_mm_map, arg_end),
+ [PR_SET_MM_ENV_START] = offsetof(struct prctl_mm_map, env_start),
+ [PR_SET_MM_ENV_END] = offsetof(struct prctl_mm_map, env_end),
+ };
+ struct prctl_mm_map prctl_map = { .exe_fd = (u32)-1, };
+ struct mm_struct *mm = current->mm;
+
+ if (arg5 || (arg4 && (opt != PR_SET_MM_AUXV &&
+ opt != PR_SET_MM_MAP &&
+ opt != PR_SET_MM_MAP_SIZE)))
+ return -EINVAL;
+
if (opt == PR_SET_MM_MAP_SIZE)
return put_user((unsigned int)sizeof(struct prctl_mm_map),
(unsigned int __user *)addr);

if (opt == PR_SET_MM_MAP) {
- struct prctl_mm_map prctl_map = { .exe_fd = (u32)-1, };
-
if (arg4 != sizeof(prctl_map))
return -EINVAL;

@@ -2068,10 +2084,43 @@ static int prctl_set_mm(int opt, unsigne

return prctl_set_mm_map(&prctl_map);
}
-#endif

- pr_warn_once("PR_SET_MM_* has been removed. Use PR_SET_MM_MAP instead\n");
- return -EINVAL;
+ if (!capable(CAP_SYS_RESOURCE))
+ return -EPERM;
+
+ if (opt == PR_SET_MM_EXE_FILE)
+ return prctl_set_mm_exe_file(mm, (unsigned int)addr);
+
+ if (opt == PR_SET_MM_AUXV)
+ return prctl_set_auxv(mm, addr, arg4);
+
+ if (opt < 1 || opt >= ARRAY_SIZE(offsets))
+ return -EINVAL;
+
+ /*
+ * Emulate PR_SET_MM_MAP call by filling with
+ * current values and setting one field from
+ * the request.
+ */
+ down_read(&mm->mmap_sem);
+ spin_lock(&mm->arg_lock);
+ prctl_map.start_code = mm->start_code;
+ prctl_map.end_code = mm->end_code;
+ prctl_map.start_data = mm->start_data;
+ prctl_map.end_data = mm->end_data;
+ prctl_map.start_brk = mm->start_brk;
+ prctl_map.brk = mm->brk;
+ prctl_map.start_stack = mm->start_stack;
+ prctl_map.arg_start = mm->arg_start;
+ prctl_map.arg_end = mm->arg_end;
+ prctl_map.env_start = mm->env_start;
+ prctl_map.env_end = mm->env_end;
+ spin_unlock(&mm->arg_lock);
+ up_read(&mm->mmap_sem);
+
+ *(unsigned long *)((char *)&prctl_map + offsets[opt]) = addr;
+
+ return prctl_set_mm_map(&prctl_map, opt);
}

#ifdef CONFIG_CHECKPOINT_RESTORE
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