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From:   Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
To:     linux-kernel@vger.kernel.org
Cc:     x86@kernel.org, mingo@redhat.com, jpoimboe@redhat.com,
        Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Subject: [PATCH] x86/unwind/orc: recheck address range after stack info was updated V2
Date:   Sun, 17 Apr 2022 16:23:11 +0300
Message-Id: <1650201791-356270-1-git-send-email-dmtrmonakhov@yandex-team.ru>
Precedence: bulk

get_stack_info() detects stack type only by begin address, so we must
check that address range in question is fully covered by detected stack

Otherwise following crash is possible:
-> unwind_next_frame
   case ORC_TYPE_REGS:
     if (!deref_stack_regs(state, sp, &state->ip, &state->sp))
     -> deref_stack_regs
       -> stack_access_ok  <- addr is ok, but addr+len-1 is not, exit with success
     *ip = READ_ONCE_NOCHECK(regs->ip); <- Here we hit stack guard fault

Original OOPS log:
BUG: stack guard page was hit at 000000000dd984a2 (stack is 00000000d1caafca..00000000613712f0)
kernel stack overflow (page fault): 0000 [#1] SMP NOPTI
CPU: 93 PID: 23787 Comm: context_switch1 Not tainted 5.4.145 #1
RIP: 0010:unwind_next_frame
Call Trace:
 <NMI>
 perf_callchain_kernel
 ..
 get_perf_callchain
 perf_callchain
 perf_prepare_sample
 perf_event_output_forward
 ...
 __perf_event_overflow
 perf_ibs_handle_irq
 ....
 perf_ibs_nmi_handler
 nmi_handle
 default_do_nmi
 do_nmi
 end_repeat_nmi

Changes since v1:
 - Do not call on_stack() twice for valid range.

Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 794fdef2501a..38185aedf7d1 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -339,11 +339,11 @@ static bool stack_access_ok(struct unwind_state *state, unsigned long _addr,
 	struct stack_info *info = &state->stack_info;
 	void *addr = (void *)_addr;
 
-	if (!on_stack(info, addr, len) &&
-	    (get_stack_info(addr, state->task, info, &state->stack_mask)))
-		return false;
+	if (on_stack(info, addr, len))
+		return true;
 
-	return true;
+	return !get_stack_info(addr, state->task, info, &state->stack_mask) &&
+		on_stack(info, addr, len);
 }
 
 static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
-- 
2.7.4