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target/i386: emulate 64-bit ring 0 for linux-user if LM feature is set

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32-bit binaries can run on a long mode processor even if the kernel
is 64-bit, of course, and this can have slightly different behavior;
for example, SYSCALL is allowed on Intel processors.

Allow reporting LM to programs running under user mode emulation,
so that "-cpu" can be used with named CPU models even for qemu-i386
and even without disabling LM by hand.

Fortunately, most of the runtime code in QEMU has to depend on HF_LMA_MASK
or on HF_CS64_MASK (which is anyway false for qemu-i386's 32-bit code
segment) rather than TARGET_X86_64, therefore all that is needed is an
update of linux-user's ring 0 setup.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1534
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2023-06-20 16:49:35 +02:00
parent d903259dd2
commit 40a205da41
3 changed files with 44 additions and 34 deletions
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57
linux-user/i386/cpu_loop.c
View file

@ -47,7 +47,7 @@ static void write_dt(void *ptr, unsigned long addr, unsigned long limit,
}
static uint64_t *idt_table;
#ifdef TARGET_X86_64
static void set_gate64(void *ptr, unsigned int type, unsigned int dpl,
uint64_t addr, unsigned int sel)
{
@ -60,8 +60,10 @@ static void set_gate64(void *ptr, unsigned int type, unsigned int dpl,
p[2] = tswap32(addr >> 32);
p[3] = 0;
}
#ifdef TARGET_X86_64
/* only dpl matters as we do only user space emulation */
static void set_idt(int n, unsigned int dpl)
static void set_idt(int n, unsigned int dpl, bool is64)
{
set_gate64(idt_table + n * 2, 0, dpl, 0, 0);
}
@ -78,9 +80,13 @@ static void set_gate(void *ptr, unsigned int type, unsigned int dpl,
}
/* only dpl matters as we do only user space emulation */
static void set_idt(int n, unsigned int dpl)
static void set_idt(int n, unsigned int dpl, bool is64)
{
set_gate(idt_table + n, 0, dpl, 0, 0);
if (is64) {
set_gate64(idt_table + n * 2, 0, dpl, 0, 0);
} else {
set_gate(idt_table + n, 0, dpl, 0, 0);
}
}
#endif
@ -325,6 +331,9 @@ static void target_cpu_free(void *obj)
void target_cpu_copy_regs(CPUArchState *env, struct target_pt_regs *regs)
{
CPUState *cpu = env_cpu(env);
bool is64 = (env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) != 0;
int i;
OBJECT(cpu)->free = target_cpu_free;
env->cr[0] = CR0_PG_MASK | CR0_WP_MASK | CR0_PE_MASK;
env->hflags |= HF_PE_MASK | HF_CPL_MASK;
@ -332,15 +341,18 @@ void target_cpu_copy_regs(CPUArchState *env, struct target_pt_regs *regs)
env->cr[4] |= CR4_OSFXSR_MASK;
env->hflags |= HF_OSFXSR_MASK;
}
#ifndef TARGET_ABI32
/* enable 64 bit mode if possible */
if (!(env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM)) {
if (is64) {
env->cr[4] |= CR4_PAE_MASK;
env->efer |= MSR_EFER_LMA | MSR_EFER_LME;
env->hflags |= HF_LMA_MASK;
}
#ifndef TARGET_ABI32
else {
fprintf(stderr, "The selected x86 CPU does not support 64 bit mode\n");
exit(EXIT_FAILURE);
}
env->cr[4] |= CR4_PAE_MASK;
env->efer |= MSR_EFER_LMA | MSR_EFER_LME;
env->hflags |= HF_LMA_MASK;
#endif
/* flags setup : we activate the IRQs by default as in user mode */
@ -379,27 +391,12 @@ void target_cpu_copy_regs(CPUArchState *env, struct target_pt_regs *regs)
PROT_READ|PROT_WRITE,
MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
idt_table = g2h_untagged(env->idt.base);
set_idt(0, 0);
set_idt(1, 0);
set_idt(2, 0);
set_idt(3, 3);
set_idt(4, 3);
set_idt(5, 0);
set_idt(6, 0);
set_idt(7, 0);
set_idt(8, 0);
set_idt(9, 0);
set_idt(10, 0);
set_idt(11, 0);
set_idt(12, 0);
set_idt(13, 0);
set_idt(14, 0);
set_idt(15, 0);
set_idt(16, 0);
set_idt(17, 0);
set_idt(18, 0);
set_idt(19, 0);
set_idt(0x80, 3);
for (i = 0; i < 20; i++) {
set_idt(i, 0, is64);
}
set_idt(3, 3, is64);
set_idt(4, 3, is64);
set_idt(0x80, 3, is64);
/* linux segment setup */
{

15
target/i386/cpu.c
View file

@ -666,7 +666,10 @@ void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
* and therefore using the 32-bit ABI; the CPU itself might be 64-bit
* but again the difference is only visible in kernel mode.
*/
#if defined CONFIG_USER_ONLY
#if defined CONFIG_LINUX_USER
#define CPUID_EXT2_KERNEL_FEATURES (CPUID_EXT2_LM | CPUID_EXT2_FFXSR)
#elif defined CONFIG_USER_ONLY
/* FIXME: Long mode not yet supported for i386 bsd-user */
#define CPUID_EXT2_KERNEL_FEATURES CPUID_EXT2_FFXSR
#else
#define CPUID_EXT2_KERNEL_FEATURES 0
@ -5539,7 +5542,15 @@ uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
}
#ifndef TARGET_X86_64
if (w == FEAT_8000_0001_EDX) {
r &= ~CPUID_EXT2_LM;
/*
* 32-bit TCG can emulate 64-bit compatibility mode. If there is no
* way for userspace to get out of its 32-bit jail, we can leave
* the LM bit set.
*/
uint32_t unavail = tcg_enabled()
? CPUID_EXT2_LM & ~CPUID_EXT2_KERNEL_FEATURES
: CPUID_EXT2_LM;
r &= ~unavail;
}
#endif
if (migratable_only) {

6
target/i386/tcg/translate.c
View file

@ -173,12 +173,14 @@ typedef struct DisasContext {
#endif
#if !defined(TARGET_X86_64)
#define CODE64(S) false
#define LMA(S) false
#elif defined(CONFIG_USER_ONLY)
#define CODE64(S) true
#define LMA(S) true
#else
#define CODE64(S) (((S)->flags & HF_CS64_MASK) != 0)
#endif
#if defined(CONFIG_SOFTMMU) && !defined(TARGET_X86_64)
#define LMA(S) false
#else
#define LMA(S) (((S)->flags & HF_LMA_MASK) != 0)
#endif