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systrap: don't copy an FPU state in sighandler

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We can set ucontext->uc_mcontext.fpregs to the memory with a target state.

PiperOrigin-RevId: 527340901
This commit is contained in:
Andrei Vagin
2023-04-26 12:27:42 -07:00
committed by gVisor bot
parent 60c3e2f0db
commit 96f2aca71f
1 changed files with 46 additions and 2 deletions
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pkg/sentry/platform/systrap/sysmsg/sighandler_amd64.c
+46 -2
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@@ -20,6 +20,7 @@
#include <linux/futex.h>
#include <linux/unistd.h>
#include <signal.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
@@ -196,6 +197,9 @@ struct thread_context *switch_context_amd64(
return ctx;
}
static void prep_fpstate_for_sigframe(void *buf, uint32_t user_size,
bool use_xsave);
void __export_sighandler(int signo, siginfo_t *siginfo, void *_ucontext) {
ucontext_t *ucontext = _ucontext;
void *sp = sysmsg_sp();
@@ -335,8 +339,10 @@ void __export_sighandler(int signo, siginfo_t *siginfo, void *_ucontext) {
if (__export_context_decoupling_exp &&
__atomic_load_n(&ctx->fpstate_changed, __ATOMIC_ACQUIRE)) {
memcpy((uint8_t *)ucontext->uc_mcontext.fpregs, ctx->fpstate,
__export_arch_state.fp_len);
prep_fpstate_for_sigframe(
ctx->fpstate, __export_arch_state.fp_len,
__export_arch_state.xsave_mode != XSAVE_MODE_FXSAVE);
ucontext->uc_mcontext.fpregs = (void *)ctx->fpstate;
}
ptregs_to_gregs(ucontext, &ctx->ptregs);
}
@@ -453,3 +459,41 @@ void verify_offsets_amd64() {
(offsetof(struct user_regs_struct, gs) + PTREGS_OFFSET));
#undef PTREGS_OFFSET
}
// asm/sigcontext.h conflicts with signal.h.
struct __fpx_sw_bytes {
uint32_t magic1;
uint32_t extended_size;
uint64_t xfeatures;
uint32_t xstate_size;
uint32_t padding[7];
};
struct __fpstate {
uint16_t cwd;
uint16_t swd;
uint16_t twd;
uint16_t fop;
uint64_t rip;
uint64_t rdp;
uint32_t mxcsr;
uint32_t mxcsr_mask;
uint32_t st_space[32];
uint32_t xmm_space[64];
uint32_t reserved2[12];
struct __fpx_sw_bytes sw_reserved;
};
// The kernel expects to see some additional info in an FPU state. More details
// can be found in arch/x86/kernel/fpu/signal.c:check_xstate_in_sigframe.
static void prep_fpstate_for_sigframe(void *buf, uint32_t user_size,
bool use_xsave) {
struct __fpstate *fpstate = buf;
struct __fpx_sw_bytes *sw_bytes = &fpstate->sw_reserved;
sw_bytes->magic1 = FP_XSTATE_MAGIC1;
sw_bytes->extended_size = user_size + FP_XSTATE_MAGIC2_SIZE;
sw_bytes->xfeatures = ~(0ULL);
sw_bytes->xstate_size = user_size;
*(uint32_t *)(buf + user_size) = use_xsave ? FP_XSTATE_MAGIC2 : 0;
}