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authorkib <kib@FreeBSD.org>2014-12-27 23:19:08 +0000
committerkib <kib@FreeBSD.org>2014-12-27 23:19:08 +0000
commitd0d6e7c817bec5a1c5f2c25cd4762b908bed2ffc (patch)
tree1132f4d5e9ee4767f431ad299e1c5015a8fd6833 /sys/amd64/ia32/ia32_syscall.c
parent509ff4169be0d36eecfc6a58cf0cb6b8a18b86e5 (diff)
downloadFreeBSD-src-d0d6e7c817bec5a1c5f2c25cd4762b908bed2ffc.zip
FreeBSD-src-d0d6e7c817bec5a1c5f2c25cd4762b908bed2ffc.tar.gz
Change the way the lcall $7,$0 is reflected to usermode. Instead of
setting call gate, which must be 64 bit, put a code segment descriptor into ldt slot 0. This way, syscall shim does not switch temporary to 64bit trampoline, and does not create a window where signal delivery interrupts 64 bit mode (signal handler cannot return). The cost is shim running with non-zero based segment in %cs, which requires vfork() handling make more assumptions. Sponsored by: The FreeBSD Foundation MFC after: 1 week
Diffstat (limited to 'sys/amd64/ia32/ia32_syscall.c')
-rw-r--r--sys/amd64/ia32/ia32_syscall.c39
1 files changed, 14 insertions, 25 deletions
diff --git a/sys/amd64/ia32/ia32_syscall.c b/sys/amd64/ia32/ia32_syscall.c
index 92249f9..6e96edd 100644
--- a/sys/amd64/ia32/ia32_syscall.c
+++ b/sys/amd64/ia32/ia32_syscall.c
@@ -223,39 +223,28 @@ int
setup_lcall_gate(void)
{
struct i386_ldt_args uap;
- struct user_segment_descriptor descs[2];
- struct gate_descriptor *ssd;
+ struct user_segment_descriptor desc;
uint32_t lcall_addr;
int error;
bzero(&uap, sizeof(uap));
uap.start = 0;
- uap.num = 2;
-
- /*
- * This is the easiest way to cut the space for system
- * descriptor in ldt. Manually adjust the descriptor type to
- * the call gate later.
- */
- bzero(&descs[0], sizeof(descs));
- descs[0].sd_type = SDT_SYSNULL;
- descs[1].sd_type = SDT_SYSNULL;
- error = amd64_set_ldt(curthread, &uap, descs);
+ uap.num = 1;
+ lcall_addr = curproc->p_sysent->sv_psstrings - sz_lcall_tramp;
+ bzero(&desc, sizeof(desc));
+ desc.sd_type = SDT_MEMERA;
+ desc.sd_dpl = SEL_UPL;
+ desc.sd_p = 1;
+ desc.sd_def32 = 1;
+ desc.sd_gran = 1;
+ desc.sd_lolimit = 0xffff;
+ desc.sd_hilimit = 0xf;
+ desc.sd_lobase = lcall_addr;
+ desc.sd_hibase = lcall_addr >> 24;
+ error = amd64_set_ldt(curthread, &uap, &desc);
if (error != 0)
return (error);
- lcall_addr = curproc->p_sysent->sv_psstrings - sz_lcall_tramp;
- mtx_lock(&dt_lock);
- ssd = (struct gate_descriptor *)(curproc->p_md.md_ldt->ldt_base);
- bzero(ssd, sizeof(*ssd));
- ssd->gd_looffset = lcall_addr;
- ssd->gd_hioffset = lcall_addr >> 16;
- ssd->gd_selector = _ucodesel;
- ssd->gd_type = SDT_SYSCGT;
- ssd->gd_dpl = SEL_UPL;
- ssd->gd_p = 1;
- mtx_unlock(&dt_lock);
-
return (0);
}
#endif
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