From 5f9552657ea9aaa3d5e8ff594555f2746432cc33 Mon Sep 17 00:00:00 2001 From: Stanislav Shmarov Date: Mon, 26 Feb 2018 02:36:00 -0500 Subject: [PATCH] target-i386: Fixed syscall posssible segfault In user-mode emulation env->idt.base memory is allocated in linux-user/main.c with size 8*512 = 4096 (for 64-bit). When fake interrupt EXCP_SYSCALL is thrown do_interrupt_user checks destination privilege level for this fake exception, and tries to read 4 bytes at address base + (256 * 2^4)=4096, that causes segfault. Privlege level was checked only for int's, so lets read dpl from memory only for this case. Backports commit 885b7c44e4f8b7a012a92770a0dba8b238662caa from qemu --- qemu/target-i386/seg_helper.c | 37 +++++++++++++++++++---------------- 1 file changed, 20 insertions(+), 17 deletions(-) diff --git a/qemu/target-i386/seg_helper.c b/qemu/target-i386/seg_helper.c index 11537fd0..57e72655 100644 --- a/qemu/target-i386/seg_helper.c +++ b/qemu/target-i386/seg_helper.c @@ -1137,25 +1137,28 @@ static void do_interrupt_real(CPUX86State *env, int intno, int is_int, static void do_interrupt_user(CPUX86State *env, int intno, int is_int, int error_code, target_ulong next_eip) { - SegmentCache *dt; - target_ulong ptr; - int dpl, cpl, shift; - uint32_t e2; + if (is_int) { + SegmentCache *dt; + target_ulong ptr; + int dpl, cpl, shift; + uint32_t e2; - dt = &env->idt; - if (env->hflags & HF_LMA_MASK) { - shift = 4; - } else { - shift = 3; - } - ptr = dt->base + (intno << shift); - e2 = cpu_ldl_kernel(env, ptr + 4); + dt = &env->idt; + if (env->hflags & HF_LMA_MASK) { + shift = 4; + } else { + shift = 3; + } + ptr = dt->base + (intno << shift); + e2 = cpu_ldl_kernel(env, ptr + 4); - dpl = (e2 >> DESC_DPL_SHIFT) & 3; - cpl = env->hflags & HF_CPL_MASK; - /* check privilege if software int */ - if (is_int && dpl < cpl) { - raise_exception_err(env, EXCP0D_GPF, (intno << shift) + 2); + + dpl = (e2 >> DESC_DPL_SHIFT) & 3; + cpl = env->hflags & HF_CPL_MASK; + /* check privilege if software int */ + if (dpl < cpl) { + raise_exception_err(env, EXCP0D_GPF, (intno << shift) + 2); + } } /* Since we emulate only user space, we cannot do more than