[PATCH v6 2/3] arm64: stacktrace: Relax frame record alignment requirement to 8 bytes

From: Peter Collingbourne <pcc@google.com>
To: Mark Brown <broonie@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	 Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	 Andrey Konovalov <andreyknvl@gmail.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Ard Biesheuvel <ardb@kernel.org>
Cc: Peter Collingbourne <pcc@google.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: [PATCH v6 2/3] arm64: stacktrace: Relax frame record alignment requirement to 8 bytes
Date: Wed, 26 May 2021 10:49:26 -0700	[thread overview]
Message-ID: <20210526174927.2477847-2-pcc@google.com> (raw)
In-Reply-To: <20210526174927.2477847-1-pcc@google.com>

The AAPCS places no requirements on the alignment of the frame
record. In theory it could be placed anywhere, although it seems
sensible to require it to be aligned to 8 bytes. With an upcoming
enhancement to tag-based KASAN Clang will begin creating frame records
located at an address that is only aligned to 8 bytes. Accommodate
such frame records in the stack unwinding code.

As pointed out by Mark Rutland, the userspace stack unwinding code
has the same problem, so fix it there as well.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/Ia22c375230e67ca055e9e4bb639383567f7ad268
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
---
v6:
- rebase onto for-next/stacktrace

v5:
- fix rebase

v4:
- rebase to 5.13rc1

v2:
- fix it in the userspace unwinding code as well

 arch/arm64/kernel/perf_callchain.c | 2 +-
 arch/arm64/kernel/stacktrace.c     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index 88ff471b0bce..4a72c2727309 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -116,7 +116,7 @@ void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
 		tail = (struct frame_tail __user *)regs->regs[29];
 
 		while (entry->nr < entry->max_stack &&
-		       tail && !((unsigned long)tail & 0xf))
+		       tail && !((unsigned long)tail & 0x7))
 			tail = user_backtrace(tail, entry);
 	} else {
 #ifdef CONFIG_COMPAT
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 5c70f247645b..b189de5ca6cb 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -75,7 +75,7 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 	if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
 		return -ENOENT;
 
-	if (fp & 0xf)
+	if (fp & 0x7)
 		return -EINVAL;
 
 	if (!on_accessible_stack(tsk, fp, 16, &info))
-- 
2.31.1.818.g46aad6cb9e-goog


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