linux-kernel - [PATCH AUTOSEL 4.4 27/44] signal: Properly deliver SIGSEGV from x86 uprobes

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Date:   Fri,  8 Nov 2019 06:47:03 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.4 27/44] signal: Properly deliver SIGSEGV from x86 uprobes

From: "Eric W. Biederman" <ebiederm@...ssion.com>

[ Upstream commit 4a63c1ffd384ebdce40aac9c997dab68379137be ]

For userspace to tell the difference between an random signal
and an exception, the exception must include siginfo information.

Using SEND_SIG_FORCED for SIGSEGV is thus wrong, and it will result in
userspace seeing si_code == SI_USER (like a random signal) instead of
si_code == SI_KERNEL or a more specific si_code as all exceptions
deliver.

Therefore replace force_sig_info(SIGSEGV, SEND_SIG_FORCE, current)
with force_sig(SIG_SEGV, current) which gets this right and is shorter
and easier to type.

Fixes: 791eca10107f ("uretprobes/x86: Hijack return address")
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kernel/uprobes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 178d63cac321b..60b12c14cf6fb 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -983,7 +983,7 @@ arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs
 		pr_err("uprobe: return address clobbered: pid=%d, %%sp=%#lx, "
 			"%%ip=%#lx\n", current->pid, regs->sp, regs->ip);

-		force_sig_info(SIGSEGV, SEND_SIG_FORCED, current);
+		force_sig(SIGSEGV, current);
 	}

 	return -1;
-- 
2.20.1