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Prevent attacker from manipulating FPU tag word used in SGX enclave #73471

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merged 2 commits into from
Jun 20, 2020
Merged

Prevent attacker from manipulating FPU tag word used in SGX enclave #73471

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Prevent attacker from manipulating FPU tag word used in SGX enclave
raoulstrackx Jun 17, 2020
33b304c
Using xsave restore to restore complete FPU state
raoulstrackx Jun 19, 2020
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20 changes: 8 additions & 12 deletions src/libstd/sys/sgx/abi/entry.S
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Original file line number Diff line number Diff line change
Expand Up @@ -26,18 +26,10 @@ IMAGE_BASE:
.Lxsave_clear:
.org .+24
.Lxsave_mxcsr:
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.int 0
.short 0x1f80

/* 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

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

Expand Down Expand Up @@ -177,13 +169,17 @@ sgx_entry:
jz .Lskip_debug_init
mov %r10,%gs:tcsls_debug_panic_buf_ptr
.Lskip_debug_init:
/* reset cpu state */
mov %rdx, %r10
mov $-1, %rax
mov $-1, %rdx
xrstor .Lxsave_clear(%rip)
mov %r10, %rdx

/* 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 Down