git: b1e2f063ae91 - main - amd64 sendsig: fix context corruption

[Konstantin Belousov]

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=b1e2f063ae912dc5b7a7f6638ccb3aff14f299cf

commit b1e2f063ae912dc5b7a7f6638ccb3aff14f299cf
Author:     Konstantin Belousov <kib at FreeBSD.org>
AuthorDate: 2021-09-27 16:57:25 +0000
Commit:     Konstantin Belousov <kib at FreeBSD.org>
CommitDate: 2021-09-27 17:12:46 +0000

    amd64 sendsig: fix context corruption
    
    Drop fpstate only after copying out xfpustate from the thread usermode
    save area. Otherwise a context switch between get_fpcontext(), which now
    returns the pointer directly into user save area, and copyout, would
    cause reinit of the save area, loosing user registers.
    
    Reported, reviewed, and tested by:      markj
    Sponsored by:   The FreeBSD Foundation
    MFC after:      3 days
    Differential revision:  https://reviews.freebsd.org/D32159
---
 sys/amd64/amd64/exec_machdep.c | 2 +-
 sys/amd64/ia32/ia32_signal.c   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/sys/amd64/amd64/exec_machdep.c b/sys/amd64/amd64/exec_machdep.c
index d605f080871a..b93fe7c4b3c7 100644
--- a/sys/amd64/amd64/exec_machdep.c
+++ b/sys/amd64/amd64/exec_machdep.c
@@ -143,7 +143,6 @@ sendsig(sig_t catcher, ksiginfo_t *ksi, sigset_t *mask)
 	bcopy(regs, &sf.sf_uc.uc_mcontext.mc_rdi, sizeof(*regs));
 	sf.sf_uc.uc_mcontext.mc_len = sizeof(sf.sf_uc.uc_mcontext); /* magic */
 	get_fpcontext(td, &sf.sf_uc.uc_mcontext, &xfpusave, &xfpusave_len);
-	fpstate_drop(td);
 	update_pcb_bases(pcb);
 	sf.sf_uc.uc_mcontext.mc_fsbase = pcb->pcb_fsbase;
 	sf.sf_uc.uc_mcontext.mc_gsbase = pcb->pcb_gsbase;
@@ -203,6 +202,7 @@ sendsig(sig_t catcher, ksiginfo_t *ksi, sigset_t *mask)
 		sigexit(td, SIGILL);
 	}
 
+	fpstate_drop(td);
 	regs->tf_rsp = (long)sfp;
 	regs->tf_rip = p->p_sysent->sv_sigcode_base;
 	regs->tf_rflags &= ~(PSL_T | PSL_D);
diff --git a/sys/amd64/ia32/ia32_signal.c b/sys/amd64/ia32/ia32_signal.c
index ab7100f5b9fb..6c879eccfc77 100644
--- a/sys/amd64/ia32/ia32_signal.c
+++ b/sys/amd64/ia32/ia32_signal.c
@@ -607,7 +607,6 @@ ia32_sendsig(sig_t catcher, ksiginfo_t *ksi, sigset_t *mask)
 	sf.sf_uc.uc_mcontext.mc_gs = regs->tf_gs;
 	sf.sf_uc.uc_mcontext.mc_len = sizeof(sf.sf_uc.uc_mcontext); /* magic */
 	ia32_get_fpcontext(td, &sf.sf_uc.uc_mcontext, &xfpusave, &xfpusave_len);
-	fpstate_drop(td);
 	sf.sf_uc.uc_mcontext.mc_fsbase = td->td_pcb->pcb_fsbase;
 	sf.sf_uc.uc_mcontext.mc_gsbase = td->td_pcb->pcb_gsbase;
 
@@ -661,6 +660,7 @@ ia32_sendsig(sig_t catcher, ksiginfo_t *ksi, sigset_t *mask)
 		sigexit(td, SIGILL);
 	}
 
+	fpstate_drop(td);
 	regs->tf_rsp = (uintptr_t)sfp;
 	regs->tf_rip = p->p_sysent->sv_sigcode_base;
 	regs->tf_rflags &= ~(PSL_T | PSL_D);