linux-kernel - [PATCH v2 2/2] LoongArch: Make do

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Message-ID: <20250422110719.15673-3-yangtiezhu@loongson.cn>
Date: Tue, 22 Apr 2025 19:07:19 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] LoongArch: Make do_xyz() handlers more robust

Currently, interrupts need to be disabled before single-step mode is set,
it requires that the CSR_PRMD_PIE must be cleared in save_local_irqflag()
which is called by setup_singlestep(), this is reasonable.

But in the first kprobe breakpoint exception, if the irq is enabled at the
beginning of do_bp(), it will not be disabled at the end of do_bp() due to
the CSR_PRMD_PIE has been cleared in save_local_irqflag(). For this case,
it may corrupt exception context when restoring exception after do_bp() in
handle_bp(), this is not reasonable.

In order to restore exception safely in handle_bp(), it needs to make sure
the irq is disabled at the end of do_bp(), so just add a local variable to
record the original interrupt status in the parent context, then use it as
check condition to enable and disable irq in do_bp().

While at it, do the similar thing for the other do_xyz() handlers to make
them more robust.

Fixes: 6d4cc40fb5f5 ("LoongArch: Add kprobes support")
Suggested-by: Jinyang He <hejinyang@...ngson.cn>
Suggested-by: Huacai Chen <chenhuacai@...ngson.cn>
Co-developed-by: Tianyang Zhang <zhangtianyang@...ngson.cn>
Signed-off-by: Tianyang Zhang <zhangtianyang@...ngson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 arch/loongarch/kernel/traps.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
index 2ec3106c0da3..7de38d34efc6 100644
--- a/arch/loongarch/kernel/traps.c
+++ b/arch/loongarch/kernel/traps.c
@@ -547,6 +547,7 @@ int no_unaligned_warning __read_mostly = 1;	/* Only 1 warning by default */
 
 asmlinkage void noinstr do_ale(struct pt_regs *regs)
 {
+	bool pie = regs_irqs_disabled(regs);
 	irqentry_state_t state = irqentry_enter(regs);
 
 #ifndef CONFIG_ARCH_STRICT_ALIGN
@@ -555,7 +556,7 @@ asmlinkage void noinstr do_ale(struct pt_regs *regs)
 #else
 	unsigned int *pc;
 
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_enable();
 
 	perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, regs->csr_badvaddr);
@@ -582,7 +583,7 @@ asmlinkage void noinstr do_ale(struct pt_regs *regs)
 	die_if_kernel("Kernel ale access", regs);
 	force_sig_fault(SIGBUS, BUS_ADRALN, (void __user *)regs->csr_badvaddr);
 out:
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_disable();
 #endif
 	irqentry_exit(regs, state);
@@ -621,12 +622,13 @@ static void bug_handler(struct pt_regs *regs)
 asmlinkage void noinstr do_bce(struct pt_regs *regs)
 {
 	bool user = user_mode(regs);
+	bool pie = regs_irqs_disabled(regs);
 	unsigned long era = exception_era(regs);
 	u64 badv = 0, lower = 0, upper = ULONG_MAX;
 	union loongarch_instruction insn;
 	irqentry_state_t state = irqentry_enter(regs);
 
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_enable();
 
 	current->thread.trap_nr = read_csr_excode();
@@ -692,7 +694,7 @@ asmlinkage void noinstr do_bce(struct pt_regs *regs)
 	force_sig_bnderr((void __user *)badv, (void __user *)lower, (void __user *)upper);
 
 out:
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_disable();
 
 	irqentry_exit(regs, state);
@@ -710,11 +712,12 @@ asmlinkage void noinstr do_bce(struct pt_regs *regs)
 asmlinkage void noinstr do_bp(struct pt_regs *regs)
 {
 	bool user = user_mode(regs);
+	bool pie = regs_irqs_disabled(regs);
 	unsigned int opcode, bcode;
 	unsigned long era = exception_era(regs);
 	irqentry_state_t state = irqentry_enter(regs);
 
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_enable();
 
 	if (__get_inst(&opcode, (u32 *)era, user))
@@ -780,7 +783,7 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
 	}
 
 out:
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_disable();
 
 	irqentry_exit(regs, state);
@@ -1015,6 +1018,7 @@ static void init_restore_lbt(void)
 
 asmlinkage void noinstr do_lbt(struct pt_regs *regs)
 {
+	bool pie = regs_irqs_disabled(regs);
 	irqentry_state_t state = irqentry_enter(regs);
 
 	/*
@@ -1024,7 +1028,7 @@ asmlinkage void noinstr do_lbt(struct pt_regs *regs)
 	 * (including the user using 'MOVGR2GCSR' to turn on TM, which
 	 * will not trigger the BTE), we need to check PRMD first.
 	 */
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_enable();
 
 	if (!cpu_has_lbt) {
@@ -1038,7 +1042,7 @@ asmlinkage void noinstr do_lbt(struct pt_regs *regs)
 	preempt_enable();
 
 out:
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_disable();
 
 	irqentry_exit(regs, state);
-- 
2.42.0