@@ -18,6 +18,16 @@
extern asmlinkage void ret_from_exception(void);
+static inline int fp_is_valid(unsigned long fp, unsigned long sp)
+{
+ unsigned long low, high;
+
+ low = sp + sizeof(struct stackframe);
+ high = ALIGN(sp, THREAD_SIZE);
+
+ return !(fp < low || fp > high || fp & 0x07);
+}
+
void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
bool (*fn)(void *, unsigned long), void *arg)
{
@@ -41,21 +51,19 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
}
for (;;) {
- unsigned long low, high;
struct stackframe *frame;
if (unlikely(!__kernel_text_address(pc) || (level++ >= 0 && !fn(arg, pc))))
break;
- /* Validate frame pointer */
- low = sp + sizeof(struct stackframe);
- high = ALIGN(sp, THREAD_SIZE);
- if (unlikely(fp < low || fp > high || fp & 0x7))
+ if (unlikely(!fp_is_valid(fp, sp)))
break;
+
/* Unwind stack frame */
frame = (struct stackframe *)fp - 1;
sp = fp;
- if (regs && (regs->epc == pc) && (frame->fp & 0x7)) {
+ if (regs && (regs->epc == pc) && fp_is_valid(frame->ra, sp))
+ /* We hit function where ra is not saved on the stack */
fp = frame->ra;
pc = regs->ra;
} else {
If the load access fault occures in a leaf function (with CONFIG_FRAME_POINTER=y), when wrong stack trace will be displayed: [<ffffffff804853c2>] regmap_mmio_read32le+0xe/0x1c ---[ end trace 0000000000000000 ]--- Registers dump: ra 0xffffffff80485758 <regmap_mmio_read+36> sp 0xffffffc80200b9a0 fp 0xffffffc80200b9b0 pc 0xffffffff804853ba <regmap_mmio_read32le+6> Stack dump: 0xffffffc80200b9a0: 0xffffffc80200b9e0 0xffffffc80200b9e0 0xffffffc80200b9b0: 0xffffffff8116d7e8 0x0000000000000100 0xffffffc80200b9c0: 0xffffffd8055b9400 0xffffffd8055b9400 0xffffffc80200b9d0: 0xffffffc80200b9f0 0xffffffff8047c526 0xffffffc80200b9e0: 0xffffffc80200ba30 0xffffffff8047fe9a The assembler dump of the function preambula: add sp,sp,-16 sd s0,8(sp) add s0,sp,16 In the fist stack frame, where ra is not stored on the stack we can observe: 0(sp) 8(sp) .---------------------------------------------. sp->| frame->fp | frame->ra (saved fp) | |---------------------------------------------| fp->| .... | .... | |---------------------------------------------| | | | and in the code check is performed: if (regs && (regs->epc == pc) && (frame->fp & 0x7)) I see no reason to check frame->fp value at all, because it is can be uninitialized value on the stack. A better way is to check frame->ra to be an address on the stack. After the stacktrace shows as expect: [<ffffffff804853c2>] regmap_mmio_read32le+0xe/0x1c [<ffffffff80485758>] regmap_mmio_read+0x24/0x52 [<ffffffff8047c526>] _regmap_bus_reg_read+0x1a/0x22 [<ffffffff8047fe9a>] _regmap_read+0x5c/0xea [<ffffffff80480376>] _regmap_update_bits+0x76/0xc0 ... ---[ end trace 0000000000000000 ]--- Fixes: f766f77a74f5 ("riscv/stacktrace: Fix stack output without ra on the stack top") Signed-off-by: Matthew Bystrin <dev.mbstr@gmail.com> --- As pointed by Samuel Holland it is incorrect to remove check of the stackframe entirely. Changes since v1 [1]: - Instead of just dropping frame->fp check, replace it with validation of frame->ra, which should be a stack address. - Move frame pointer validation into the separate function. [1] https://lore.kernel.org/linux-riscv/20240426072701.6463-1-dev.mbstr@gmail.com/ arch/riscv/kernel/stacktrace.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-)