archives/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-03-08 02:44:41 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions

objtool, xen: Fix INSN_SYSCALL / INSN_SYSRET semantics

Browse source 
Objtool uses an arbitrary rule for INSN_SYSCALL and INSN_SYSRET that
almost works by accident: if it's in a function, control flow continues
after the instruction, otherwise it terminates.

That behavior should instead be based on the semantics of the underlying
instruction.  Change INSN_SYSCALL to always preserve control flow and
INSN_SYSRET to always terminate it.

The changed semantic for INSN_SYSCALL requires a tweak to the
!CONFIG_IA32_EMULATION version of xen_entry_SYSCALL_compat().  In Xen,
SYSCALL is a hypercall which usually returns.  But in this case it's a
hypercall to IRET which doesn't return.  Add UD2 to tell objtool to
terminate control flow, and to prevent undefined behavior at runtime.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com> # for the Xen part
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/19453dfe9a0431b7f016e9dc16d031cad3812a50.1744095216.git.jpoimboe@kernel.org
This commit is contained in:
Josh Poimboeuf 2025-04-08 00:02:16 -07:00 • committed by Ingo Molnar
parent 9f9cc012c2
commit 2dbbca9be4
2 changed files with 15 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

4
arch/x86/xen/xen-asm.S
View file

@ -226,9 +226,7 @@ SYM_CODE_END(xen_early_idt_handler_array)
push %rax
mov $__HYPERVISOR_iret, %eax
syscall /* Do the IRET. */
#ifdef CONFIG_MITIGATION_SLS
int3
#endif
ud2 /* The SYSCALL should never return. */
.endm
SYM_CODE_START(xen_iret)

23
tools/objtool/check.c
View file

@ -3685,14 +3685,19 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
break;
case INSN_SYSCALL:
case INSN_SYSRET:
if (func) {
if (!next_insn || !next_insn->hint) {
WARN_INSN(insn, "unsupported instruction in callable function");
return 1;
}
break;
if (func && (!next_insn || !next_insn->hint)) {
WARN_INSN(insn, "unsupported instruction in callable function");
return 1;
}
break;
case INSN_SYSRET:
if (func && (!next_insn || !next_insn->hint)) {
WARN_INSN(insn, "unsupported instruction in callable function");
return 1;
}
return 0;
case INSN_STAC:
@ -3888,9 +3893,9 @@ static int validate_unret(struct objtool_file *file, struct instruction *insn)
return 1;
case INSN_SYSCALL:
break;
case INSN_SYSRET:
if (insn_func(insn))
break;
return 0;
case INSN_NOP: