6.6-stable review patch. If anyone has any objections, please let me know.
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From: Matthew Bystrin dev.mbstr@gmail.com
[ Upstream commit a2a4d4a6a0bf5eba66f8b0b32502cc20d82715a0 ]
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 ]--- As pointed by Samuel Holland it is incorrect to remove check of the stackframe entirely.
Changes since v2 [2]: - Add accidentally forgotten curly brace
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.co... [2] https://lore.kernel.org/linux-riscv/20240521131314.48895-1-dev.mbstr@gmail.c...
Fixes: f766f77a74f5 ("riscv/stacktrace: Fix stack output without ra on the stack top") Signed-off-by: Matthew Bystrin dev.mbstr@gmail.com Reviewed-by: Samuel Holland samuel.holland@sifive.com Link: https://lore.kernel.org/r/20240521191727.62012-1-dev.mbstr@gmail.com Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/kernel/stacktrace.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-)
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c index 64a9c093aef93..528ec7cc9a622 100644 --- a/arch/riscv/kernel/stacktrace.c +++ b/arch/riscv/kernel/stacktrace.c @@ -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 {