git: 4ea65707d370 - main - exec_new_vmspace: print useful error message on ctty if stack cannot be mapped.

[Konstantin Belousov]

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=4ea65707d3700efe250868a7a581b87fd96f635c

commit 4ea65707d3700efe250868a7a581b87fd96f635c
Author:     Konstantin Belousov <kib at FreeBSD.org>
AuthorDate: 2021-01-11 18:51:07 +0000
Commit:     Konstantin Belousov <kib at FreeBSD.org>
CommitDate: 2021-01-11 23:15:43 +0000

    exec_new_vmspace: print useful error message on ctty if stack cannot be mapped.
    
    After old vmspace is destroyed during execve(2), but before the new space
    is fully constructed, an error during image activation cannot be returned
    because there is no executing program to receive it.
    
    In the relatively common case of failure to map stack, print some hints
    on the control terminal.  Note that user has enough knobs to cause stack
    mapping error, and this is the most common reason for execve(2) aborting
    the process.
    
    Requested by:   jhb
    Reviewed by:    emaste, jhb
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D28050
---
 sys/kern/kern_exec.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index 13753177127f..3de6ac565db5 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -1043,6 +1043,7 @@ exec_new_vmspace(struct image_params *imgp, struct sysentvec *sv)
 	struct rlimit rlim_stack;
 	vm_offset_t sv_minuser, stack_addr;
 	vm_map_t map;
+	vm_prot_t stack_prot;
 	u_long ssiz;
 
 	imgp->vmspace_destroyed = 1;
@@ -1126,11 +1127,16 @@ exec_new_vmspace(struct image_params *imgp, struct sysentvec *sv)
 	if (ssiz < imgp->eff_stack_sz)
 		imgp->eff_stack_sz = ssiz;
 	stack_addr = sv->sv_usrstack - ssiz;
-	error = vm_map_stack(map, stack_addr, (vm_size_t)ssiz,
-	    obj != NULL && imgp->stack_prot != 0 ? imgp->stack_prot :
-	    sv->sv_stackprot, VM_PROT_ALL, MAP_STACK_GROWS_DOWN);
-	if (error != KERN_SUCCESS)
+	stack_prot = obj != NULL && imgp->stack_prot != 0 ?
+	    imgp->stack_prot : sv->sv_stackprot;
+	error = vm_map_stack(map, stack_addr, (vm_size_t)ssiz, stack_prot,
+	    VM_PROT_ALL, MAP_STACK_GROWS_DOWN);
+	if (error != KERN_SUCCESS) {
+		uprintf("exec_new_vmspace: mapping stack size %#jx prot %#x "
+		    "failed mach error %d errno %d\n", (uintmax_t)ssiz,
+		    stack_prot, error, vm_mmap_to_errno(error));
 		return (vm_mmap_to_errno(error));
+	}
 
 	/*
 	 * vm_ssize and vm_maxsaddr are somewhat antiquated concepts, but they