[PATCH 4.19 164/422] signal: Properly deliver SIGSEGV from x86 uprobes

From: Greg Kroah-Hartman
Date: Tue Nov 19 2019 - 01:08:32 EST

From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>

[ 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

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@xxxxxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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 9119859ba7871..420aa7d3a2e6b 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -1089,7 +1089,7 @@ arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs
pr_err("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;