The branch releng/15.0 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=57a2373f86acf8e2dbb334776044c7c1122a7432
commit 57a2373f86acf8e2dbb334776044c7c1122a7432 Author: Mark Johnston <[email protected]> AuthorDate: 2026-08-24 14:57:16 +0000 Commit: Mark Johnston <[email protected]> CommitDate: 2026-08-24 19:29:46 +0000 hwpmc: Fix the execve handler When a process execve()s, pmc_process_exec() is supposed to evaluate whether the new image is setuid/setgid and if so, whether to detach PMCs. This was handled by pmc_can_attach(), which is effectively an open-coded copy of cr_xids_subset(). Unfortunately, the test of the result of this function was inverted, with the result that we'd detach PMCs only if the predicate said it was okay to do so. It appears the bug has always been there; it seems the intent was to return 0 on "success", i.e., it is okay to attach the PMCs, much like p_candebug(). Commits 1c3c698ba4c4 and 1c40b15971f0 obscured this a bit. I think this check is trying to be too clever. Let's make it simpler: simply do not attach PMCs unless the owner is privileged. This is how, e.g., ktrace works. I do not think it's worth trying to be more sophisticated than this unless we can generalize the policy in a way that's applicable to other subsystems. Also fix a bug at the end of pmc_process_exec(): pmc_detach_one_process() will call pmc_remove_process_descriptor() for us. Approved by: so Security: FreeBSD-SA-26:56.hwpmc Security: CVE-2026-58089 Reported by: netchild Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D59102 --- sys/dev/hwpmc/hwpmc_mod.c | 72 ++++++++--------------------------------------- sys/kern/kern_exec.c | 2 +- 2 files changed, 13 insertions(+), 61 deletions(-) diff --git a/sys/dev/hwpmc/hwpmc_mod.c b/sys/dev/hwpmc/hwpmc_mod.c index a6a6ae68996c..50baff47e504 100644 --- a/sys/dev/hwpmc/hwpmc_mod.c +++ b/sys/dev/hwpmc/hwpmc_mod.c @@ -210,7 +210,6 @@ static int pmc_attach_one_process(struct proc *p, struct pmc *pm); static bool pmc_can_allocate_row(int ri, enum pmc_mode mode); static bool pmc_can_allocate_rowindex(struct proc *p, unsigned int ri, int cpu); -static bool pmc_can_attach(struct pmc *pm, struct proc *p); static void pmc_capture_user_callchain(int cpu, int soft, struct trapframe *tf); static void pmc_cleanup(void); @@ -1025,60 +1024,6 @@ pmc_unlink_target_process(struct pmc *pm, struct pmc_process *pp) } } -/* - * Check if PMC 'pm' may be attached to target process 't'. - */ - -static bool -pmc_can_attach(struct pmc *pm, struct proc *t) -{ - struct proc *o; /* pmc owner */ - struct ucred *oc, *tc; /* owner, target credentials */ - bool decline_attach; - - /* - * A PMC's owner can always attach that PMC to itself. - */ - - if ((o = pm->pm_owner->po_owner) == t) - return (true); - - PROC_LOCK(o); - oc = o->p_ucred; - crhold(oc); - PROC_UNLOCK(o); - - PROC_LOCK(t); - tc = t->p_ucred; - crhold(tc); - PROC_UNLOCK(t); - - /* - * The effective uid of the PMC owner should match at least one - * of the {effective,real,saved} uids of the target process. - */ - - decline_attach = oc->cr_uid != tc->cr_uid && - oc->cr_uid != tc->cr_svuid && - oc->cr_uid != tc->cr_ruid; - - /* - * Every one of the target's group ids, must be in the owner's - * group list. - */ - for (int i = 0; !decline_attach && i < tc->cr_ngroups; i++) - decline_attach = !groupmember(tc->cr_groups[i], oc); - if (!decline_attach) - decline_attach = !groupmember(tc->cr_gid, oc) || - !groupmember(tc->cr_rgid, oc) || - !groupmember(tc->cr_svgid, oc); - - crfree(tc); - crfree(oc); - - return (!decline_attach); -} - /* * Attach a process to a PMC. */ @@ -1411,10 +1356,19 @@ pmc_process_exec(struct thread *td, struct pmckern_procexec *pk) */ for (ri = 0; ri < md->pmd_npmc; ri++) { if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL) { - if (pmc_can_attach(pm, td->td_proc)) { + struct proc *owner; + struct ucred *cred; + + owner = pm->pm_owner->po_owner; + PROC_LOCK(owner); + cred = crhold(owner->p_ucred); + PROC_UNLOCK(owner); + + if (priv_check_cred(cred, PRIV_DEBUG_DIFFCRED) != 0) pmc_detach_one_process(td->td_proc, pm, PMC_FLAG_NONE); - } + + crfree(cred); } } @@ -1427,10 +1381,8 @@ pmc_process_exec(struct thread *td, struct pmckern_procexec *pk) * PMCs, we can remove the process entry and free * up space. */ - if (pp->pp_refcnt == 0) { - pmc_remove_process_descriptor(pp); + if (pp->pp_refcnt == 0) pmc_destroy_process_descriptor(pp); - } } /* diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c index 3dc3e54ee762..3df2701fabc4 100644 --- a/sys/kern/kern_exec.c +++ b/sys/kern/kern_exec.c @@ -1008,7 +1008,7 @@ interpret: */ if (PMC_SYSTEM_SAMPLING_ACTIVE() || PMC_PROC_IS_USING_PMCS(p)) { VOP_UNLOCK(imgp->vp); - pe.pm_credentialschanged = credential_changing; + pe.pm_credentialschanged = imgp->credential_setid; pe.pm_baseaddr = imgp->reloc_base; pe.pm_dynaddr = imgp->et_dyn_addr;
