Previously a program could switch to a compat mode segment and then
execute SYSCALL and it would jump to an uninitialized MSR and crash
the kernel.
Instead supply a dummy target for this case.
Pointed out by Jan Beulich
Cc: [email protected]
Signed-off-by: Andi Kleen <[email protected]>
---
arch/x86_64/kernel/entry.S | 7 +++++++
arch/x86_64/kernel/setup64.c | 3 +++
2 files changed, 10 insertions(+)
Index: linux/arch/x86_64/kernel/entry.S
===================================================================
--- linux.orig/arch/x86_64/kernel/entry.S
+++ linux/arch/x86_64/kernel/entry.S
@@ -1163,3 +1163,10 @@ ENTRY(call_softirq)
ret
CFI_ENDPROC
ENDPROC(call_softirq)
+
+KPROBE_ENTRY(ignore_sysret)
+ CFI_STARTPROC
+ mov $-ENOSYS,%eax
+ sysret
+ CFI_ENDPROC
+ENDPROC(ignore_sysret)
Index: linux/arch/x86_64/kernel/setup64.c
===================================================================
--- linux.orig/arch/x86_64/kernel/setup64.c
+++ linux/arch/x86_64/kernel/setup64.c
@@ -150,6 +150,8 @@ void pda_init(int cpu)
char boot_exception_stacks[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]
__attribute__((section(".bss.page_aligned")));
+extern asmlinkage void ignore_sysret(void);
+
/* May not be marked __init: used by software suspend */
void syscall_init(void)
{
@@ -160,6 +162,7 @@ void syscall_init(void)
*/
wrmsrl(MSR_STAR, ((u64)__USER32_CS)<<48 | ((u64)__KERNEL_CS)<<32);
wrmsrl(MSR_LSTAR, system_call);
+ wrmsrl(MSR_CSTAR, ignore_sysret);
#ifdef CONFIG_IA32_EMULATION
syscall32_cpu_init ();
-
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