MIPS: fix FP mode selection in lieu of .MIPS.abiflags data (620b1550) · Commits · 戴 / test

Commit ("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>

arch/mips/kernel/elf.c

+17 −15

Original line number	Diff line number	Diff line
		@@ -76,14 +76,6 @@ int arch_elf_pt_proc(void _ehdr, void _phdr, struct file *elf,

		/* Lets see if this is an O32 ELF */
		if (ehdr32->e_ident[EI_CLASS] == ELFCLASS32) {
		/* FR = 1 for N32 */
		if (ehdr32->e_flags & EF_MIPS_ABI2)
		state->overall_fp_mode = FP_FR1;
		else
		/* Set a good default FPU mode for O32 */
		state->overall_fp_mode = cpu_has_mips_r6 ?
		FP_FRE : FP_FR0;

		if (ehdr32->e_flags & EF_MIPS_FP64) {
		/*
		* Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will override it
		@@ -104,9 +96,6 @@ int arch_elf_pt_proc(void _ehdr, void _phdr, struct file *elf,
		(char *)&abiflags,
		sizeof(abiflags));
		} else {
		/* FR=1 is really the only option for 64-bit */
		state->overall_fp_mode = FP_FR1;

		if (phdr64->p_type != PT_MIPS_ABIFLAGS)
		return 0;
		if (phdr64->p_filesz < sizeof(abiflags))
		@@ -137,6 +126,7 @@ int arch_check_elf(void *_ehdr, bool has_interpreter,
		struct elf32_hdr *ehdr = _ehdr;
		struct mode_req prog_req, interp_req;
		int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
		bool is_mips64;

		if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
		return 0;
		@@ -152,10 +142,22 @@ int arch_check_elf(void *_ehdr, bool has_interpreter,
		abi0 = abi1 = fp_abi;
		}

		/* ABI limits. O32 = FP_64A, N32/N64 = FP_SOFT */
		max_abi = ((ehdr->e_ident[EI_CLASS] == ELFCLASS32) &&
		(!(ehdr->e_flags & EF_MIPS_ABI2))) ?
		MIPS_ABI_FP_64A : MIPS_ABI_FP_SOFT;
		is_mips64 = (ehdr->e_ident[EI_CLASS] == ELFCLASS64) \|\|
		(ehdr->e_flags & EF_MIPS_ABI2);

		if (is_mips64) {
		/* MIPS64 code always uses FR=1, thus the default is easy */
		state->overall_fp_mode = FP_FR1;

		/* Disallow access to the various FPXX & FP64 ABIs */
		max_abi = MIPS_ABI_FP_SOFT;
		} else {
		/* Default to a mode capable of running code expecting FR=0 */
		state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0;

		/* Allow all ABIs we know about */
		max_abi = MIPS_ABI_FP_64A;
		}

		if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) \|\|
		(abi1 > max_abi && abi1 != MIPS_ABI_FP_UNKNOWN))

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