linux/arch/mips/kernel/elf.c
Xi Ruoyao 59be5c3585 mips: Call lose_fpu(0) before initializing fcr31 in mips_set_personality_nan
If we still own the FPU after initializing fcr31, when we are preempted
the dirty value in the FPU will be read out and stored into fcr31,
clobbering our setting.  This can cause an improper floating-point
environment after execve().  For example:

    zsh% cat measure.c
    #include <fenv.h>
    int main() { return fetestexcept(FE_INEXACT); }
    zsh% cc measure.c -o measure -lm
    zsh% echo $((1.0/3)) # raising FE_INEXACT
    0.33333333333333331
    zsh% while ./measure; do ; done
    (stopped in seconds)

Call lose_fpu(0) before setting fcr31 to prevent this.

Closes: https://lore.kernel.org/linux-mips/7a6aa1bbdbbe2e63ae96ff163fab0349f58f1b9e.camel@xry111.site/
Fixes: 9b26616c8d ("MIPS: Respect the ISA level in FCSR handling")
Cc: stable@vger.kernel.org
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
2024-01-27 11:08:04 +01:00

344 lines
9.5 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Copyright (C) 2014 Imagination Technologies
* Author: Paul Burton <paul.burton@mips.com>
*/
#include <linux/binfmts.h>
#include <linux/elf.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <asm/cpu-features.h>
#include <asm/cpu-info.h>
#include <asm/fpu.h>
#ifdef CONFIG_MIPS_FP_SUPPORT
/* Whether to accept legacy-NaN and 2008-NaN user binaries. */
bool mips_use_nan_legacy;
bool mips_use_nan_2008;
/* FPU modes */
enum {
FP_FRE,
FP_FR0,
FP_FR1,
};
/**
* struct mode_req - ABI FPU mode requirements
* @single: The program being loaded needs an FPU but it will only issue
* single precision instructions meaning that it can execute in
* either FR0 or FR1.
* @soft: The soft(-float) requirement means that the program being
* loaded needs has no FPU dependency at all (i.e. it has no
* FPU instructions).
* @fr1: The program being loaded depends on FPU being in FR=1 mode.
* @frdefault: The program being loaded depends on the default FPU mode.
* That is FR0 for O32 and FR1 for N32/N64.
* @fre: The program being loaded depends on FPU with FRE=1. This mode is
* a bridge which uses FR=1 whilst still being able to maintain
* full compatibility with pre-existing code using the O32 FP32
* ABI.
*
* More information about the FP ABIs can be found here:
*
* https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking#10.4.1._Basic_mode_set-up
*
*/
struct mode_req {
bool single;
bool soft;
bool fr1;
bool frdefault;
bool fre;
};
static const struct mode_req fpu_reqs[] = {
[MIPS_ABI_FP_ANY] = { true, true, true, true, true },
[MIPS_ABI_FP_DOUBLE] = { false, false, false, true, true },
[MIPS_ABI_FP_SINGLE] = { true, false, false, false, false },
[MIPS_ABI_FP_SOFT] = { false, true, false, false, false },
[MIPS_ABI_FP_OLD_64] = { false, false, false, false, false },
[MIPS_ABI_FP_XX] = { false, false, true, true, true },
[MIPS_ABI_FP_64] = { false, false, true, false, false },
[MIPS_ABI_FP_64A] = { false, false, true, false, true }
};
/*
* Mode requirements when .MIPS.abiflags is not present in the ELF.
* Not present means that everything is acceptable except FR1.
*/
static struct mode_req none_req = { true, true, false, true, true };
int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
bool is_interp, struct arch_elf_state *state)
{
union {
struct elf32_hdr e32;
struct elf64_hdr e64;
} *ehdr = _ehdr;
struct elf32_phdr *phdr32 = _phdr;
struct elf64_phdr *phdr64 = _phdr;
struct mips_elf_abiflags_v0 abiflags;
bool elf32;
u32 flags;
int ret;
loff_t pos;
elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
/* Let's see if this is an O32 ELF */
if (elf32) {
if (flags & EF_MIPS_FP64) {
/*
* Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will override it
* later if needed
*/
if (is_interp)
state->interp_fp_abi = MIPS_ABI_FP_OLD_64;
else
state->fp_abi = MIPS_ABI_FP_OLD_64;
}
if (phdr32->p_type != PT_MIPS_ABIFLAGS)
return 0;
if (phdr32->p_filesz < sizeof(abiflags))
return -EINVAL;
pos = phdr32->p_offset;
} else {
if (phdr64->p_type != PT_MIPS_ABIFLAGS)
return 0;
if (phdr64->p_filesz < sizeof(abiflags))
return -EINVAL;
pos = phdr64->p_offset;
}
ret = kernel_read(elf, &abiflags, sizeof(abiflags), &pos);
if (ret < 0)
return ret;
if (ret != sizeof(abiflags))
return -EIO;
/* Record the required FP ABIs for use by mips_check_elf */
if (is_interp)
state->interp_fp_abi = abiflags.fp_abi;
else
state->fp_abi = abiflags.fp_abi;
return 0;
}
int arch_check_elf(void *_ehdr, bool has_interpreter, void *_interp_ehdr,
struct arch_elf_state *state)
{
union {
struct elf32_hdr e32;
struct elf64_hdr e64;
} *ehdr = _ehdr;
union {
struct elf32_hdr e32;
struct elf64_hdr e64;
} *iehdr = _interp_ehdr;
struct mode_req prog_req, interp_req;
int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
bool elf32;
u32 flags;
elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
/*
* Determine the NaN personality, reject the binary if not allowed.
* Also ensure that any interpreter matches the executable.
*/
if (flags & EF_MIPS_NAN2008) {
if (mips_use_nan_2008)
state->nan_2008 = 1;
else
return -ENOEXEC;
} else {
if (mips_use_nan_legacy)
state->nan_2008 = 0;
else
return -ENOEXEC;
}
if (has_interpreter) {
bool ielf32;
u32 iflags;
ielf32 = iehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
iflags = ielf32 ? iehdr->e32.e_flags : iehdr->e64.e_flags;
if ((flags ^ iflags) & EF_MIPS_NAN2008)
return -ELIBBAD;
}
if (!IS_ENABLED(CONFIG_MIPS_O32_FP64_SUPPORT))
return 0;
fp_abi = state->fp_abi;
if (has_interpreter) {
interp_fp_abi = state->interp_fp_abi;
abi0 = min(fp_abi, interp_fp_abi);
abi1 = max(fp_abi, interp_fp_abi);
} else {
abi0 = abi1 = fp_abi;
}
if (elf32 && !(flags & EF_MIPS_ABI2)) {
/* 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;
} else {
/* 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;
}
if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) ||
(abi1 > max_abi && abi1 != MIPS_ABI_FP_UNKNOWN))
return -ELIBBAD;
/* It's time to determine the FPU mode requirements */
prog_req = (abi0 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi0];
interp_req = (abi1 == MIPS_ABI_FP_UNKNOWN) ? none_req : fpu_reqs[abi1];
/*
* Check whether the program's and interp's ABIs have a matching FPU
* mode requirement.
*/
prog_req.single = interp_req.single && prog_req.single;
prog_req.soft = interp_req.soft && prog_req.soft;
prog_req.fr1 = interp_req.fr1 && prog_req.fr1;
prog_req.frdefault = interp_req.frdefault && prog_req.frdefault;
prog_req.fre = interp_req.fre && prog_req.fre;
/*
* Determine the desired FPU mode
*
* Decision making:
*
* - We want FR_FRE if FRE=1 and both FR=1 and FR=0 are false. This
* means that we have a combination of program and interpreter
* that inherently require the hybrid FP mode.
* - If FR1 and FRDEFAULT is true, that means we hit the any-abi or
* fpxx case. This is because, in any-ABI (or no-ABI) we have no FPU
* instructions so we don't care about the mode. We will simply use
* the one preferred by the hardware. In fpxx case, that ABI can
* handle both FR=1 and FR=0, so, again, we simply choose the one
* preferred by the hardware. Next, if we only use single-precision
* FPU instructions, and the default ABI FPU mode is not good
* (ie single + any ABI combination), we set again the FPU mode to the
* one is preferred by the hardware. Next, if we know that the code
* will only use single-precision instructions, shown by single being
* true but frdefault being false, then we again set the FPU mode to
* the one that is preferred by the hardware.
* - We want FP_FR1 if that's the only matching mode and the default one
* is not good.
* - Return with -ELIBADD if we can't find a matching FPU mode.
*/
if (prog_req.fre && !prog_req.frdefault && !prog_req.fr1)
state->overall_fp_mode = FP_FRE;
else if ((prog_req.fr1 && prog_req.frdefault) ||
(prog_req.single && !prog_req.frdefault))
/* Make sure 64-bit MIPS III/IV/64R1 will not pick FR1 */
state->overall_fp_mode = ((raw_current_cpu_data.fpu_id & MIPS_FPIR_F64) &&
cpu_has_mips_r2_r6) ?
FP_FR1 : FP_FR0;
else if (prog_req.fr1)
state->overall_fp_mode = FP_FR1;
else if (!prog_req.fre && !prog_req.frdefault &&
!prog_req.fr1 && !prog_req.single && !prog_req.soft)
return -ELIBBAD;
return 0;
}
static inline void set_thread_fp_mode(int hybrid, int regs32)
{
if (hybrid)
set_thread_flag(TIF_HYBRID_FPREGS);
else
clear_thread_flag(TIF_HYBRID_FPREGS);
if (regs32)
set_thread_flag(TIF_32BIT_FPREGS);
else
clear_thread_flag(TIF_32BIT_FPREGS);
}
void mips_set_personality_fp(struct arch_elf_state *state)
{
/*
* This function is only ever called for O32 ELFs so we should
* not be worried about N32/N64 binaries.
*/
if (!IS_ENABLED(CONFIG_MIPS_O32_FP64_SUPPORT))
return;
switch (state->overall_fp_mode) {
case FP_FRE:
set_thread_fp_mode(1, 0);
break;
case FP_FR0:
set_thread_fp_mode(0, 1);
break;
case FP_FR1:
set_thread_fp_mode(0, 0);
break;
default:
BUG();
}
}
/*
* Select the IEEE 754 NaN encoding and ABS.fmt/NEG.fmt execution mode
* in FCSR according to the ELF NaN personality.
*/
void mips_set_personality_nan(struct arch_elf_state *state)
{
struct cpuinfo_mips *c = &boot_cpu_data;
struct task_struct *t = current;
/* Do this early so t->thread.fpu.fcr31 won't be clobbered in case
* we are preempted before the lose_fpu(0) in start_thread.
*/
lose_fpu(0);
t->thread.fpu.fcr31 = c->fpu_csr31;
switch (state->nan_2008) {
case 0:
break;
case 1:
if (!(c->fpu_msk31 & FPU_CSR_NAN2008))
t->thread.fpu.fcr31 |= FPU_CSR_NAN2008;
if (!(c->fpu_msk31 & FPU_CSR_ABS2008))
t->thread.fpu.fcr31 |= FPU_CSR_ABS2008;
break;
default:
BUG();
}
}
#endif /* CONFIG_MIPS_FP_SUPPORT */
int mips_elf_read_implies_exec(void *elf_ex, int exstack)
{
/*
* Set READ_IMPLIES_EXEC only on non-NX systems that
* do not request a specific state via PT_GNU_STACK.
*/
return (!cpu_has_rixi && exstack == EXSTACK_DEFAULT);
}
EXPORT_SYMBOL(mips_elf_read_implies_exec);