LoongArch: Enable exception fixup for specific ADE subcode

This patch allows the LoongArch BPF JIT to handle recoverable memory
access errors generated by BPF_PROBE_MEM* instructions.

When a BPF program performs memory access operations, the instructions
it executes may trigger ADEM exceptions. The kernel’s built-in BPF
exception table mechanism (EX_TYPE_BPF) will generate corresponding
exception fixup entries in the JIT compilation phase; however, the
architecture-specific trap handling function needs to proactively call
the common fixup routine to achieve exception recovery.

do_ade(): fix EX_TYPE_BPF memory access exceptions for BPF programs,
ensure safe execution.

Relevant test cases: illegal address access tests in module_attach and
subprogs_extable of selftests/bpf.

Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: Chenghao Duan

arch/loongarch/kernel/traps.c

@@ -535,10 +535,15 @@ asmlinkage void noinstr do_fpe(struct pt_regs *regs, unsigned long fcsr)
 asmlinkage void noinstr do_ade(struct pt_regs *regs)
 {
 	irqentry_state_t state = irqentry_enter(regs);
+	unsigned int esubcode = FIELD_GET(CSR_ESTAT_ESUBCODE, regs->csr_estat);
+
+	if ((esubcode == EXSUBCODE_ADEM) && fixup_exception(regs))
+		goto out;
 
 	die_if_kernel("Kernel ade access", regs);
 	force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)regs->csr_badvaddr);
 
+out:
 	irqentry_exit(regs, state);
 }