[PATCH 4.0 122/148] MIPS: fix FP mode selection in lieu of .MIPS.abiflags data

Greg Kroah-Hartman
2015-06-03T12:23:50Z

From: Paul Burton <paul.burton@imgtec.com>

commit 620b155034570f577470cf5309f741bac6a6e32b upstream.

Commit 46490b572544 ("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
Patchwork: http://patchwork.linux-mips.org/patch/9978/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/mips/kernel/elf.c | 32 +++++++++++++++++---------------
1 file changed, 17 insertions(+), 15 deletions(-)

--- a/arch/mips/kernel/elf.c
+++ b/arch/mips/kernel/elf.c
@@ -76,14 +76,6 @@ int arch_elf_pt_proc(void *_ehdr, void *

/* 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 *
(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))
@@ -147,6 +136,7 @@ int arch_check_elf(void *_ehdr, bool has
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;
@@ -162,10 +152,22 @@ int arch_check_elf(void *_ehdr, bool has
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))