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Christian Brauner
5de6dbf291
A transparent binfmt_misc dispatch hands the binary to the interpreter
through AT_EXECFD and leaves the argument vector exactly as the caller
built it. The loader on the receiving end has to know which contract it
got.
On the classic 'O'/'C' entries the binary's path is spliced into the
argument vector and the loader consumes arguments. In transparent mode
nothing was spliced and argv belongs entirely to the program. This
cannot be inferred from AT_EXECFD alone. Raise a new AT_FLAGS bit
following the AT_FLAGS_PRESERVE_ARGV0 precedent added for qemu-user in
commit 2347961b11 ("binfmt_misc: pass binfmt_misc flags to the
interpreter").
The bit also announces that mm->exe_file names the binary rather than
the interpreter (added in the next commit). A loader that sees the bit
may finish the identity polish by fixing up AT_PHDR/AT_ENTRY/AT_BASE in
saved_auxv and fix the code/data markers via one uncapped PR_SET_MM_MAP
once it has mapped the binary. I've got glibc patches for this as well
but it's useful for any loader.
BINPRM_FLAGS_TRANSPARENT_INTERP carries the mode from binfmt_misc to the
ELF loaders. Both had their own copy of the AT_FLAGS translation, so
give them one bprm_at_flags() to share instead of a second copy that can
drift. Nothing sets the bprm flag yet.
Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-8-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
33 lines
1.0 KiB
C
33 lines
1.0 KiB
C
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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#ifndef _UAPI_LINUX_BINFMTS_H
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#define _UAPI_LINUX_BINFMTS_H
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#include <linux/capability.h>
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struct pt_regs;
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/*
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* These are the maximum length and maximum number of strings passed to the
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* execve() system call. MAX_ARG_STRLEN is essentially random but serves to
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* prevent the kernel from being unduly impacted by misaddressed pointers.
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* MAX_ARG_STRINGS is chosen to fit in a signed 32-bit integer.
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*/
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#define MAX_ARG_STRLEN (PAGE_SIZE * 32)
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#define MAX_ARG_STRINGS 0x7FFFFFFF
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/* sizeof(linux_binprm->buf) */
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#define BINPRM_BUF_SIZE 256
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/* preserve argv0 for the interpreter */
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#define AT_FLAGS_PRESERVE_ARGV0_BIT 0
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#define AT_FLAGS_PRESERVE_ARGV0 (1 << AT_FLAGS_PRESERVE_ARGV0_BIT)
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/*
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* The interpreter runs transparently: the argument vector and the exe
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* link belong to the binary passed in AT_EXECFD.
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*/
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#define AT_FLAGS_TRANSPARENT_INTERP_BIT 1
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#define AT_FLAGS_TRANSPARENT_INTERP (1 << AT_FLAGS_TRANSPARENT_INTERP_BIT)
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#endif /* _UAPI_LINUX_BINFMTS_H */
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