![Paul Burton](/assets/img/avatar_default.png)
Commit 46490b5725
("MIPS: kernel: elf: Improve the overall ABI and FPU
mode checks") reworked the ELF FP ABI mode selection logic, but when
CONFIG_MIPS_O32_FP64_SUPPORT is enabled it breaks the use of binaries
which have no PT_MIPS_ABIFLAGS program header & associated
.MIPS.abiflags section.
A default mode is selected based upon whether the ELF contains MIPS32 or
MIPS64 code, but that selection is made in arch_elf_pt_proc.
arch_elf_pt_proc only executes when a PT_MIPS_ABIFLAGS program header is
found. If one is not found then arch_elf_pt_proc is never called, and no
default overall_fp_mode value is selected. When arch_check_elf is
called, both abi0 & abi1 are MIPS_ABI_FP_UNKNOWN which leads to both
prog_req & interp_req being set to none_req. none_req matches none of
the conditions for mode selection at the end of arch_check_elf, so
overall_fp_mode is left untouched. Finally once mips_set_personality_fp
is called the BUG() in the default case is then hit & the kernel likely
panics.
Fix this by moving the selection of a default overall mode to the start
of arch_check_elf, which runs once per ELF executed regardless of
whether it has a PT_MIPS_ABIFLAGS program header.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: Matthew Fortune <matthew.fortune@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org # v4.0+
Patchwork: http://patchwork.linux-mips.org/patch/9978/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
257 lines
7.6 KiB
C
257 lines
7.6 KiB
C
/*
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* Copyright (C) 2014 Imagination Technologies
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* Author: Paul Burton <paul.burton@imgtec.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* option) any later version.
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*/
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#include <linux/elf.h>
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#include <linux/sched.h>
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/* FPU modes */
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enum {
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FP_FRE,
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FP_FR0,
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FP_FR1,
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};
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/**
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* struct mode_req - ABI FPU mode requirements
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* @single: The program being loaded needs an FPU but it will only issue
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* single precision instructions meaning that it can execute in
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* either FR0 or FR1.
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* @soft: The soft(-float) requirement means that the program being
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* loaded needs has no FPU dependency at all (i.e. it has no
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* FPU instructions).
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* @fr1: The program being loaded depends on FPU being in FR=1 mode.
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* @frdefault: The program being loaded depends on the default FPU mode.
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* That is FR0 for O32 and FR1 for N32/N64.
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* @fre: The program being loaded depends on FPU with FRE=1. This mode is
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* a bridge which uses FR=1 whilst still being able to maintain
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* full compatibility with pre-existing code using the O32 FP32
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* ABI.
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*
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* More information about the FP ABIs can be found here:
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*
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* https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#10.4.1._Basic_mode_set-up
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*
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*/
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struct mode_req {
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bool single;
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bool soft;
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bool fr1;
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bool frdefault;
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bool fre;
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};
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static const struct mode_req fpu_reqs[] = {
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[MIPS_ABI_FP_ANY] = { true, true, true, true, true },
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[MIPS_ABI_FP_DOUBLE] = { false, false, false, true, true },
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[MIPS_ABI_FP_SINGLE] = { true, false, false, false, false },
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[MIPS_ABI_FP_SOFT] = { false, true, false, false, false },
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[MIPS_ABI_FP_OLD_64] = { false, false, false, false, false },
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[MIPS_ABI_FP_XX] = { false, false, true, true, true },
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[MIPS_ABI_FP_64] = { false, false, true, false, false },
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[MIPS_ABI_FP_64A] = { false, false, true, false, true }
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};
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/*
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* Mode requirements when .MIPS.abiflags is not present in the ELF.
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* Not present means that everything is acceptable except FR1.
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*/
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static struct mode_req none_req = { true, true, false, true, true };
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int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
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bool is_interp, struct arch_elf_state *state)
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{
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struct elf32_hdr *ehdr32 = _ehdr;
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struct elf32_phdr *phdr32 = _phdr;
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struct elf64_phdr *phdr64 = _phdr;
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struct mips_elf_abiflags_v0 abiflags;
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int ret;
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/* Lets see if this is an O32 ELF */
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if (ehdr32->e_ident[EI_CLASS] == ELFCLASS32) {
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if (ehdr32->e_flags & EF_MIPS_FP64) {
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/*
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* Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will override it
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* later if needed
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*/
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if (is_interp)
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state->interp_fp_abi = MIPS_ABI_FP_OLD_64;
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else
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state->fp_abi = MIPS_ABI_FP_OLD_64;
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}
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if (phdr32->p_type != PT_MIPS_ABIFLAGS)
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return 0;
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if (phdr32->p_filesz < sizeof(abiflags))
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return -EINVAL;
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ret = kernel_read(elf, phdr32->p_offset,
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(char *)&abiflags,
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sizeof(abiflags));
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} else {
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if (phdr64->p_type != PT_MIPS_ABIFLAGS)
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return 0;
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if (phdr64->p_filesz < sizeof(abiflags))
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return -EINVAL;
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ret = kernel_read(elf, phdr64->p_offset,
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(char *)&abiflags,
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sizeof(abiflags));
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}
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if (ret < 0)
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return ret;
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if (ret != sizeof(abiflags))
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return -EIO;
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/* Record the required FP ABIs for use by mips_check_elf */
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if (is_interp)
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state->interp_fp_abi = abiflags.fp_abi;
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else
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state->fp_abi = abiflags.fp_abi;
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return 0;
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}
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int arch_check_elf(void *_ehdr, bool has_interpreter,
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struct arch_elf_state *state)
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{
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struct elf32_hdr *ehdr = _ehdr;
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struct mode_req prog_req, interp_req;
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int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
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bool is_mips64;
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if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
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return 0;
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fp_abi = state->fp_abi;
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if (has_interpreter) {
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interp_fp_abi = state->interp_fp_abi;
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abi0 = min(fp_abi, interp_fp_abi);
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abi1 = max(fp_abi, interp_fp_abi);
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} else {
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abi0 = abi1 = fp_abi;
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}
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is_mips64 = (ehdr->e_ident[EI_CLASS] == ELFCLASS64) ||
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(ehdr->e_flags & EF_MIPS_ABI2);
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if (is_mips64) {
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/* MIPS64 code always uses FR=1, thus the default is easy */
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state->overall_fp_mode = FP_FR1;
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/* Disallow access to the various FPXX & FP64 ABIs */
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max_abi = MIPS_ABI_FP_SOFT;
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} else {
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/* Default to a mode capable of running code expecting FR=0 */
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state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0;
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/* Allow all ABIs we know about */
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max_abi = MIPS_ABI_FP_64A;
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}
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if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) ||
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(abi1 > max_abi && abi1 != MIPS_ABI_FP_UNKNOWN))
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return -ELIBBAD;
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/* It's time to determine the FPU mode requirements */
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prog_req = (abi0 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi0];
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interp_req = (abi1 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi1];
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/*
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* Check whether the program's and interp's ABIs have a matching FPU
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* mode requirement.
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*/
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prog_req.single = interp_req.single && prog_req.single;
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prog_req.soft = interp_req.soft && prog_req.soft;
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prog_req.fr1 = interp_req.fr1 && prog_req.fr1;
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prog_req.frdefault = interp_req.frdefault && prog_req.frdefault;
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prog_req.fre = interp_req.fre && prog_req.fre;
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/*
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* Determine the desired FPU mode
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*
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* Decision making:
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*
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* - We want FR_FRE if FRE=1 and both FR=1 and FR=0 are false. This
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* means that we have a combination of program and interpreter
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* that inherently require the hybrid FP mode.
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* - If FR1 and FRDEFAULT is true, that means we hit the any-abi or
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* fpxx case. This is because, in any-ABI (or no-ABI) we have no FPU
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* instructions so we don't care about the mode. We will simply use
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* the one preferred by the hardware. In fpxx case, that ABI can
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* handle both FR=1 and FR=0, so, again, we simply choose the one
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* preferred by the hardware. Next, if we only use single-precision
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* FPU instructions, and the default ABI FPU mode is not good
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* (ie single + any ABI combination), we set again the FPU mode to the
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* one is preferred by the hardware. Next, if we know that the code
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* will only use single-precision instructions, shown by single being
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* true but frdefault being false, then we again set the FPU mode to
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* the one that is preferred by the hardware.
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* - We want FP_FR1 if that's the only matching mode and the default one
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* is not good.
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* - Return with -ELIBADD if we can't find a matching FPU mode.
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*/
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if (prog_req.fre && !prog_req.frdefault && !prog_req.fr1)
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state->overall_fp_mode = FP_FRE;
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else if ((prog_req.fr1 && prog_req.frdefault) ||
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(prog_req.single && !prog_req.frdefault))
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/* Make sure 64-bit MIPS III/IV/64R1 will not pick FR1 */
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state->overall_fp_mode = ((current_cpu_data.fpu_id & MIPS_FPIR_F64) &&
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cpu_has_mips_r2_r6) ?
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FP_FR1 : FP_FR0;
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else if (prog_req.fr1)
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state->overall_fp_mode = FP_FR1;
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else if (!prog_req.fre && !prog_req.frdefault &&
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!prog_req.fr1 && !prog_req.single && !prog_req.soft)
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return -ELIBBAD;
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return 0;
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}
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static inline void set_thread_fp_mode(int hybrid, int regs32)
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{
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if (hybrid)
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set_thread_flag(TIF_HYBRID_FPREGS);
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else
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clear_thread_flag(TIF_HYBRID_FPREGS);
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if (regs32)
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set_thread_flag(TIF_32BIT_FPREGS);
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else
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clear_thread_flag(TIF_32BIT_FPREGS);
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}
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void mips_set_personality_fp(struct arch_elf_state *state)
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{
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/*
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* This function is only ever called for O32 ELFs so we should
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* not be worried about N32/N64 binaries.
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*/
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if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
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return;
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switch (state->overall_fp_mode) {
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case FP_FRE:
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set_thread_fp_mode(1, 0);
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break;
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case FP_FR0:
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set_thread_fp_mode(0, 1);
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break;
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case FP_FR1:
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set_thread_fp_mode(0, 0);
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break;
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default:
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BUG();
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}
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}
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