MIPS: math-emu: Make microMIPS branch delay slot emulation work
Complement commit 102cedc32a6e ("MIPS: microMIPS: Floating point
support.") which introduced microMIPS FPU emulation, but did not adjust
the encoding of the BREAK instruction used to terminate the branch delay
slot emulation frame. Consequently the execution of any such frame is
indeterminate and, depending on CPU configuration, will result in random
code execution or an offending program being terminated with SIGILL.
This is because the regular MIPS BREAK instruction is encoded with the 0
major and the 0xd minor opcode, however in the microMIPS instruction set
this major/minor opcode pair denotes an encoding reserved for the DSP
ASE. Instead the microMIPS BREAK instruction is encoded with the 0
major and the 0x7 minor opcode.
Use the correct BREAK encoding for microMIPS FPU emulation then.
Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12174/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/include/asm/fpu_emulator.h b/arch/mips/include/asm/fpu_emulator.h
index 2f021cd..3225c3c 100644
--- a/arch/mips/include/asm/fpu_emulator.h
+++ b/arch/mips/include/asm/fpu_emulator.h
@@ -79,7 +79,7 @@
/*
* Break instruction with special math emu break code set
*/
-#define BREAK_MATH (0x0000000d | (BRK_MEMU << 16))
+#define BREAK_MATH(micromips) (((micromips) ? 0x7 : 0xd) | (BRK_MEMU << 16))
#define SIGNALLING_NAN 0x7ff800007ff80000LL
diff --git a/arch/mips/include/asm/mips-r2-to-r6-emul.h b/arch/mips/include/asm/mips-r2-to-r6-emul.h
index 4b89f28..1f6ea83 100644
--- a/arch/mips/include/asm/mips-r2-to-r6-emul.h
+++ b/arch/mips/include/asm/mips-r2-to-r6-emul.h
@@ -52,7 +52,7 @@
__this_cpu_inc(mipsr2emustats.M); \
err = __get_user(nir, (u32 __user *)regs->cp0_epc); \
if (!err) { \
- if (nir == BREAK_MATH) \
+ if (nir == BREAK_MATH(0)) \
__this_cpu_inc(mipsr2bdemustats.M); \
} \
preempt_enable(); \
diff --git a/arch/mips/math-emu/dsemul.c b/arch/mips/math-emu/dsemul.c
index 4e30bfc..32ec5d7 100644
--- a/arch/mips/math-emu/dsemul.c
+++ b/arch/mips/math-emu/dsemul.c
@@ -38,6 +38,7 @@
*/
int mips_dsemul(struct pt_regs *regs, mips_instruction ir, unsigned long cpc)
{
+ mips_instruction break_math;
struct emuframe __user *fr;
int err;
@@ -65,6 +66,7 @@
* branches, but gives us a cleaner interface to the exception
* handler (single entry point).
*/
+ break_math = BREAK_MATH(get_isa16_mode(regs->cp0_epc));
/* Ensure that the two instructions are in the same cache line */
fr = (struct emuframe __user *)
@@ -79,13 +81,13 @@
(u16 __user *)(&fr->emul));
err |= __put_user(ir & 0xffff,
(u16 __user *)((long)(&fr->emul) + 2));
- err |= __put_user(BREAK_MATH >> 16,
+ err |= __put_user(break_math >> 16,
(u16 __user *)(&fr->badinst));
- err |= __put_user(BREAK_MATH & 0xffff,
+ err |= __put_user(break_math & 0xffff,
(u16 __user *)((long)(&fr->badinst) + 2));
} else {
err = __put_user(ir, &fr->emul);
- err |= __put_user((mips_instruction)BREAK_MATH, &fr->badinst);
+ err |= __put_user(break_math, &fr->badinst);
}
err |= __put_user((mips_instruction)BD_COOKIE, &fr->cookie);
@@ -139,7 +141,8 @@
}
err |= __get_user(cookie, &fr->cookie);
- if (unlikely(err || (insn != BREAK_MATH) || (cookie != BD_COOKIE))) {
+ if (unlikely(err || insn != BREAK_MATH(get_isa16_mode(xcp->cp0_epc)) ||
+ cookie != BD_COOKIE)) {
MIPS_FPU_EMU_INC_STATS(errors);
return 0;
}