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Cleanup SGX entry code #69040

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Merged
merged 3 commits into from
Feb 13, 2020
Merged

Cleanup SGX entry code #69040

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aeedc9d
Corrected ac_mitigation patch. That patch used the untrusted stack to…
raoulstrackx Feb 7, 2020
236ab6e
sanitize MXCSR/FPU control registers
raoulstrackx Feb 7, 2020
71b9ed4
Avoid jumping to Rust code with user %rsp (reentry_panic)
Feb 10, 2020
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39 changes: 29 additions & 10 deletions src/libstd/sys/sgx/abi/entry.S
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,14 @@ IMAGE_BASE:

/* We can store a bunch of data in the gap between MXCSR and the XSAVE header */

/* MXCSR initialization value for ABI */
.Lmxcsr_init:
.int 0x1f80

/* x87 FPU control word initialization value for ABI */
.Lfpucw_init:
.int 0x037f
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This is setting one of the reserved bits (6th) to 1?

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This is the default from the Intel SDM, Vol. 1, §8.1.5


/* The following symbols point at read-only data that will be filled in by the */
/* post-linker. */

Expand Down Expand Up @@ -134,6 +142,19 @@ elf_entry:
ud2 /* should not be reached */
/* end elf_entry */

/* This code needs to be called *after* the enclave stack has been setup. */
/* There are 3 places where this needs to happen, so this is put in a macro. */
.macro entry_sanitize_final
/* Sanitize rflags received from user */
/* - DF flag: x86-64 ABI requires DF to be unset at function entry/exit */
/* - AC flag: AEX on misaligned memory accesses leaks side channel info */
pushfq
andq $~0x40400, (%rsp)
popfq
bt $0,.Laborted(%rip)
jc .Lreentry_panic
.endm

.text
.global sgx_entry
.type sgx_entry,function
Expand All @@ -150,25 +171,18 @@ sgx_entry:
stmxcsr %gs:tcsls_user_mxcsr
fnstcw %gs:tcsls_user_fcw

/* reset user state */
/* - DF flag: x86-64 ABI requires DF to be unset at function entry/exit */
/* - AC flag: AEX on misaligned memory accesses leaks side channel info */
pushfq
andq $~0x40400, (%rsp)
popfq

/* check for debug buffer pointer */
testb $0xff,DEBUG(%rip)
jz .Lskip_debug_init
mov %r10,%gs:tcsls_debug_panic_buf_ptr
.Lskip_debug_init:
/* check for abort */
bt $0,.Laborted(%rip)
jc .Lreentry_panic
/* check if returning from usercall */
mov %gs:tcsls_last_rsp,%r11
test %r11,%r11
jnz .Lusercall_ret
/* reset user state */
ldmxcsr .Lmxcsr_init(%rip)
fldcw .Lfpucw_init(%rip)
/* setup stack */
mov %gs:tcsls_tos,%rsp /* initially, RSP is not set to the correct value */
/* here. This is fixed below under "adjust stack". */
Expand All @@ -179,6 +193,7 @@ sgx_entry:
lea IMAGE_BASE(%rip),%rax
add %rax,%rsp
mov %rsp,%gs:tcsls_tos
entry_sanitize_final
/* call tcs_init */
/* store caller-saved registers in callee-saved registers */
mov %rdi,%rbx
Expand All @@ -194,7 +209,10 @@ sgx_entry:
mov %r13,%rdx
mov %r14,%r8
mov %r15,%r9
jmp .Lafter_init
.Lskip_init:
entry_sanitize_final
.Lafter_init:
/* call into main entry point */
load_tcsls_flag_secondary_bool cx /* RCX = entry() argument: secondary: bool */
call entry /* RDI, RSI, RDX, R8, R9 passed in from userspace */
Expand Down Expand Up @@ -295,6 +313,7 @@ usercall:
ldmxcsr (%rsp)
fldcw 4(%rsp)
add $8, %rsp
entry_sanitize_final
pop %rbx
pop %rbp
pop %r12
Expand Down