arm64: insn: remove BUG_ON from codegen

During code generation, we used to BUG_ON unknown/unsupported encoding
or invalid parameters.

Instead, now we report these as errors and simply return the
instruction AARCH64_BREAK_FAULT. Users of these codegen helpers should
check for and handle this failure condition as appropriate.

Otherwise, unhandled codegen failure will result in trapping at
run-time due to AARCH64_BREAK_FAULT, which is arguably better than a
BUG_ON.

Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 112 insertions, 53 deletions

diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index c08b9ad6f429..7371455160e5 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -2,7 +2,7 @@
  * Copyright (C) 2013 Huawei Ltd.
  * Author: Jiang Liu <liuj97@gmail.com>
  *
- * Copyright (C) 2014 Zi Shen Lim <zlim.lnx@gmail.com>
+ * Copyright (C) 2014-2016 Zi Shen Lim <zlim.lnx@gmail.com>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -363,6 +363,9 @@ u32 __kprobes aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
         u32 immlo, immhi, mask;
         int shift;
 
+        if (insn == AARCH64_BREAK_FAULT)
+                return AARCH64_BREAK_FAULT;
+
         switch (type) {
         case AARCH64_INSN_IMM_ADR:
                 shift = 0;
@@ -377,7 +380,7 @@ u32 __kprobes aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
                 if (aarch64_get_imm_shift_mask(type, &mask, &shift) < 0) {
                         pr_err("aarch64_insn_encode_immediate: unknown immediate encoding %d\n",
                                type);
-                        return 0;
+                        return AARCH64_BREAK_FAULT;
                 }
         }
 
@@ -394,9 +397,12 @@ static u32 aarch64_insn_encode_register(enum aarch64_insn_register_type type,
 {
         int shift;
 
+        if (insn == AARCH64_BREAK_FAULT)
+                return AARCH64_BREAK_FAULT;
+
         if (reg < AARCH64_INSN_REG_0 || reg > AARCH64_INSN_REG_SP) {
                 pr_err("%s: unknown register encoding %d\n", __func__, reg);
-                return 0;
+                return AARCH64_BREAK_FAULT;
         }
 
         switch (type) {
@@ -417,7 +423,7 @@ static u32 aarch64_insn_encode_register(enum aarch64_insn_register_type type,
         default:
                 pr_err("%s: unknown register type encoding %d\n", __func__,
                        type);
-                return 0;
+                return AARCH64_BREAK_FAULT;
         }
 
         insn &= ~(GENMASK(4, 0) << shift);
@@ -446,7 +452,7 @@ static u32 aarch64_insn_encode_ldst_size(enum aarch64_insn_size_type type,
                 break;
         default:
                 pr_err("%s: unknown size encoding %d\n", __func__, type);
-                return 0;
+                return AARCH64_BREAK_FAULT;
         }
 
         insn &= ~GENMASK(31, 30);
@@ -460,14 +466,17 @@ static inline long branch_imm_common(unsigned long pc, unsigned long addr,
 {
         long offset;
 
-        /*
-         * PC: A 64-bit Program Counter holding the address of the current
-         * instruction. A64 instructions must be word-aligned.
-         */
-        BUG_ON((pc & 0x3) || (addr & 0x3));
+        if ((pc & 0x3) || (addr & 0x3)) {
+                pr_err("%s: A64 instructions must be word aligned\n", __func__);
+                return range;
+        }
 
         offset = ((long)addr - (long)pc);
-        BUG_ON(offset < -range || offset >= range);
+
+        if (offset < -range || offset >= range) {
+                pr_err("%s: offset out of range\n", __func__);
+                return range;
+        }
 
         return offset;
 }
@@ -484,6 +493,8 @@ u32 __kprobes aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
          * texts are within +/-128M.
          */
         offset = branch_imm_common(pc, addr, SZ_128M);
+        if (offset >= SZ_128M)
+                return AARCH64_BREAK_FAULT;
 
         switch (type) {
         case AARCH64_INSN_BRANCH_LINK:
@@ -493,7 +504,7 @@ u32 __kprobes aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
                 insn = aarch64_insn_get_b_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown branch encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -510,6 +521,8 @@ u32 aarch64_insn_gen_comp_branch_imm(unsigned long pc, unsigned long addr,
         long offset;
 
         offset = branch_imm_common(pc, addr, SZ_1M);
+        if (offset >= SZ_1M)
+                return AARCH64_BREAK_FAULT;
 
         switch (type) {
         case AARCH64_INSN_BRANCH_COMP_ZERO:
@@ -519,7 +532,7 @@ u32 aarch64_insn_gen_comp_branch_imm(unsigned long pc, unsigned long addr,
                 insn = aarch64_insn_get_cbnz_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown branch encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -530,7 +543,7 @@ u32 aarch64_insn_gen_comp_branch_imm(unsigned long pc, unsigned long addr,
                 insn |= AARCH64_INSN_SF_BIT;
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -550,7 +563,10 @@ u32 aarch64_insn_gen_cond_branch_imm(unsigned long pc, unsigned long addr,
 
         insn = aarch64_insn_get_bcond_value();
 
-        BUG_ON(cond < AARCH64_INSN_COND_EQ || cond > AARCH64_INSN_COND_AL);
+        if (cond < AARCH64_INSN_COND_EQ || cond > AARCH64_INSN_COND_AL) {
+                pr_err("%s: unknown condition encoding %d\n", __func__, cond);
+                return AARCH64_BREAK_FAULT;
+        }
         insn |= cond;
 
         return aarch64_insn_encode_immediate(AARCH64_INSN_IMM_19, insn,
@@ -583,7 +599,7 @@ u32 aarch64_insn_gen_branch_reg(enum aarch64_insn_register reg,
                 insn = aarch64_insn_get_ret_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown branch encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -606,7 +622,7 @@ u32 aarch64_insn_gen_load_store_reg(enum aarch64_insn_register reg,
                 insn = aarch64_insn_get_str_reg_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown load/store encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -645,26 +661,30 @@ u32 aarch64_insn_gen_load_store_pair(enum aarch64_insn_register reg1,
                 insn = aarch64_insn_get_stp_post_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown load/store encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
         switch (variant) {
         case AARCH64_INSN_VARIANT_32BIT:
-                /* offset must be multiples of 4 in the range [-256, 252] */
-                BUG_ON(offset & 0x3);
-                BUG_ON(offset < -256 || offset > 252);
+                if ((offset & 0x3) || (offset < -256) || (offset > 252)) {
+                        pr_err("%s: offset must be multiples of 4 in the range of [-256, 252] %d\n",
+                               __func__, offset);
+                        return AARCH64_BREAK_FAULT;
+                }
                 shift = 2;
                 break;
         case AARCH64_INSN_VARIANT_64BIT:
-                /* offset must be multiples of 8 in the range [-512, 504] */
-                BUG_ON(offset & 0x7);
-                BUG_ON(offset < -512 || offset > 504);
+                if ((offset & 0x7) || (offset < -512) || (offset > 504)) {
+                        pr_err("%s: offset must be multiples of 8 in the range of [-512, 504] %d\n",
+                               __func__, offset);
+                        return AARCH64_BREAK_FAULT;
+                }
                 shift = 3;
                 insn |= AARCH64_INSN_SF_BIT;
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -702,7 +722,7 @@ u32 aarch64_insn_gen_add_sub_imm(enum aarch64_insn_register dst,
                 insn = aarch64_insn_get_subs_imm_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown add/sub encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -713,11 +733,14 @@ u32 aarch64_insn_gen_add_sub_imm(enum aarch64_insn_register dst,
                 insn |= AARCH64_INSN_SF_BIT;
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
-        BUG_ON(imm & ~(SZ_4K - 1));
+        if (imm & ~(SZ_4K - 1)) {
+                pr_err("%s: invalid immediate encoding %d\n", __func__, imm);
+                return AARCH64_BREAK_FAULT;
+        }
 
         insn = aarch64_insn_encode_register(AARCH64_INSN_REGTYPE_RD, insn, dst);
 
@@ -746,7 +769,7 @@ u32 aarch64_insn_gen_bitfield(enum aarch64_insn_register dst,
                 insn = aarch64_insn_get_sbfm_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown bitfield encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -759,12 +782,18 @@ u32 aarch64_insn_gen_bitfield(enum aarch64_insn_register dst,
                 mask = GENMASK(5, 0);
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
-        BUG_ON(immr & ~mask);
-        BUG_ON(imms & ~mask);
+        if (immr & ~mask) {
+                pr_err("%s: invalid immr encoding %d\n", __func__, immr);
+                return AARCH64_BREAK_FAULT;
+        }
+        if (imms & ~mask) {
+                pr_err("%s: invalid imms encoding %d\n", __func__, imms);
+                return AARCH64_BREAK_FAULT;
+        }
 
         insn = aarch64_insn_encode_register(AARCH64_INSN_REGTYPE_RD, insn, dst);
 
@@ -793,23 +822,33 @@ u32 aarch64_insn_gen_movewide(enum aarch64_insn_register dst,
                 insn = aarch64_insn_get_movn_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown movewide encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
-        BUG_ON(imm & ~(SZ_64K - 1));
+        if (imm & ~(SZ_64K - 1)) {
+                pr_err("%s: invalid immediate encoding %d\n", __func__, imm);
+                return AARCH64_BREAK_FAULT;
+        }
 
         switch (variant) {
         case AARCH64_INSN_VARIANT_32BIT:
-                BUG_ON(shift != 0 && shift != 16);
+                if (shift != 0 && shift != 16) {
+                        pr_err("%s: invalid shift encoding %d\n", __func__,
+                               shift);
+                        return AARCH64_BREAK_FAULT;
+                }
                 break;
         case AARCH64_INSN_VARIANT_64BIT:
                 insn |= AARCH64_INSN_SF_BIT;
-                BUG_ON(shift != 0 && shift != 16 && shift != 32 &&
-                       shift != 48);
+                if (shift != 0 && shift != 16 && shift != 32 && shift != 48) {
+                        pr_err("%s: invalid shift encoding %d\n", __func__,
+                               shift);
+                        return AARCH64_BREAK_FAULT;
+                }
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -843,20 +882,28 @@ u32 aarch64_insn_gen_add_sub_shifted_reg(enum aarch64_insn_register dst,
                 insn = aarch64_insn_get_subs_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown add/sub encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
         switch (variant) {
         case AARCH64_INSN_VARIANT_32BIT:
-                BUG_ON(shift & ~(SZ_32 - 1));
+                if (shift & ~(SZ_32 - 1)) {
+                        pr_err("%s: invalid shift encoding %d\n", __func__,
+                               shift);
+                        return AARCH64_BREAK_FAULT;
+                }
                 break;
         case AARCH64_INSN_VARIANT_64BIT:
                 insn |= AARCH64_INSN_SF_BIT;
-                BUG_ON(shift & ~(SZ_64 - 1));
+                if (shift & ~(SZ_64 - 1)) {
+                        pr_err("%s: invalid shift encoding %d\n", __func__,
+                               shift);
+                        return AARCH64_BREAK_FAULT;
+                }
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -885,11 +932,15 @@ u32 aarch64_insn_gen_data1(enum aarch64_insn_register dst,
                 insn = aarch64_insn_get_rev32_value();
                 break;
         case AARCH64_INSN_DATA1_REVERSE_64:
-                BUG_ON(variant != AARCH64_INSN_VARIANT_64BIT);
+                if (variant != AARCH64_INSN_VARIANT_64BIT) {
+                        pr_err("%s: invalid variant for reverse64 %d\n",
+                               __func__, variant);
+                        return AARCH64_BREAK_FAULT;
+                }
                 insn = aarch64_insn_get_rev64_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown data1 encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -900,7 +951,7 @@ u32 aarch64_insn_gen_data1(enum aarch64_insn_register dst,
                 insn |= AARCH64_INSN_SF_BIT;
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -937,7 +988,7 @@ u32 aarch64_insn_gen_data2(enum aarch64_insn_register dst,
                 insn = aarch64_insn_get_rorv_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown data2 encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -948,7 +999,7 @@ u32 aarch64_insn_gen_data2(enum aarch64_insn_register dst,
                 insn |= AARCH64_INSN_SF_BIT;
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -976,7 +1027,7 @@ u32 aarch64_insn_gen_data3(enum aarch64_insn_register dst,
                 insn = aarch64_insn_get_msub_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown data3 encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -987,7 +1038,7 @@ u32 aarch64_insn_gen_data3(enum aarch64_insn_register dst,
                 insn |= AARCH64_INSN_SF_BIT;
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }
 
@@ -1037,20 +1088,28 @@ u32 aarch64_insn_gen_logical_shifted_reg(enum aarch64_insn_register dst,
                 insn = aarch64_insn_get_bics_value();
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown logical encoding %d\n", __func__, type);
                 return AARCH64_BREAK_FAULT;
         }
 
         switch (variant) {
         case AARCH64_INSN_VARIANT_32BIT:
-                BUG_ON(shift & ~(SZ_32 - 1));
+                if (shift & ~(SZ_32 - 1)) {
+                        pr_err("%s: invalid shift encoding %d\n", __func__,
+                               shift);
+                        return AARCH64_BREAK_FAULT;
+                }
                 break;
         case AARCH64_INSN_VARIANT_64BIT:
                 insn |= AARCH64_INSN_SF_BIT;
-                BUG_ON(shift & ~(SZ_64 - 1));
+                if (shift & ~(SZ_64 - 1)) {
+                        pr_err("%s: invalid shift encoding %d\n", __func__,
+                               shift);
+                        return AARCH64_BREAK_FAULT;
+                }
                 break;
         default:
-                BUG_ON(1);
+                pr_err("%s: unknown variant encoding %d\n", __func__, variant);
                 return AARCH64_BREAK_FAULT;
         }