um: Store full CSGSFS and SS register from mcontext

[ Upstream commit cef721e0d53d2b64f2ba177c63a0dfdd7c0daf17 ]

Doing this allows using registers as retrieved from an mcontext to be
pushed to a process using PTRACE_SETREGS.

It is not entirely clear to me why CSGSFS was masked. Doing so creates
issues when using the mcontext as process state in seccomp and simply
copying the register appears to work perfectly fine for ptrace.

Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
Link: https://patch.msgid.link/20250224181827.647129-2-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/um/os-Linux/mcontext.c b/arch/x86/um/os-Linux/mcontext.c
index e80ab7d281177b887adddd30d4f8312adca569ed..1b0d95328b2c72ac93f36652bf65cba1d1b0e2b4 100644 (file)
--- a/arch/x86/um/os-Linux/mcontext.c
+++ b/arch/x86/um/os-Linux/mcontext.c
@@ -27,7 +27,6 @@ void get_regs_from_mc(struct uml_pt_regs *regs, mcontext_t *mc)
        COPY(RIP);
        COPY2(EFLAGS, EFL);
        COPY2(CS, CSGSFS);
-       regs->gp[CS / sizeof(unsigned long)] &= 0xffff;
-       regs->gp[CS / sizeof(unsigned long)] |= 3;
+       regs->gp[SS / sizeof(unsigned long)] = mc->gregs[REG_CSGSFS] >> 48;
 #endif
 }