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target-i386: Fixed syscall posssible segfault

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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
This commit is contained in:
Stanislav Shmarov 2018-02-26 02:36:00 -05:00 committed by Lioncash
parent d8d0d08262
commit 5f9552657e
No known key found for this signature in database
GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 20 additions and 17 deletions
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5
qemu/target-i386/seg_helper.c
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@ -1137,6 +1137,7 @@ 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)
{
if (is_int) {
SegmentCache *dt;
target_ulong ptr;
int dpl, cpl, shift;
@ -1151,12 +1152,14 @@ static void do_interrupt_user(CPUX86State *env, int intno, int is_int,
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) {
if (dpl < cpl) {
raise_exception_err(env, EXCP0D_GPF, (intno << shift) + 2);
}
}
/* Since we emulate only user space, we cannot do more than
exiting the emulation with the suitable exception and error