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[RFC,1/9] um: Store full CSGSFS and SS register from mcontext

Message ID 20240925203232.565086-2-benjamin@sipsolutions.net
State RFC
Headers show
Series SECCOMP based userspace for UML | expand

Commit Message

Benjamin Berg Sept. 25, 2024, 8:32 p.m. UTC 
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>
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
---
 arch/x86/um/os-Linux/mcontext.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
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Patch

diff --git a/arch/x86/um/os-Linux/mcontext.c b/arch/x86/um/os-Linux/mcontext.c
index e80ab7d28117..1b0d95328b2c 100644
--- 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
 }