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amd64: less code and data in the upper half

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Call jumpToKernel() in sysret()/iret() so that there is less
code and data in the upper half, and, especially, current
goroutine's stack and user regs will not be accessed from the
upper half (also with the help from previous patches which make
less code in userCR3 context).

jumpToUser() will not be needed, because current goroutine's stack
and return value in the stack is lower half address.

It is prepared for KPTI for gvisor.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antfin.com>
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
This commit is contained in:
Lai Jiangshan
2020-08-04 18:27:32 +08:00
committed by Lai Jiangshan
parent 5a0f2f6e49
commit c4d364c7ce
5 changed files with 26 additions and 39 deletions
Download Patch File Download Diff File Expand all files Collapse all files
pkg/sentry/platform/ring0/entry_amd64.go
+3
View File
@@ -36,6 +36,9 @@ func sysenter()
// This must be called prior to sysret/iret.
func swapgs()
// jumpToKernel jumps to the kernel version of the current RIP.
func jumpToKernel()
// sysret returns to userspace from a system call.
//
// The return code is the vector that interrupted execution.
pkg/sentry/platform/ring0/entry_amd64.s
+23 -6
View File
@@ -104,11 +104,24 @@ TEXT ·swapgs(SB),NOSPLIT,$0
SWAP_GS()
RET
// jumpToKernel changes execution to the kernel address space.
//
// This works by changing the return value to the kernel version.
TEXT ·jumpToKernel(SB),NOSPLIT,$0
MOVQ 0(SP), AX
ORQ ·KernelStartAddress(SB), AX // Future return value.
MOVQ AX, 0(SP)
RET
// See entry_amd64.go.
TEXT ·sysret(SB),NOSPLIT,$0-24
// Save original state.
LOAD_KERNEL_ADDRESS(cpu+0(FP), BX)
LOAD_KERNEL_ADDRESS(regs+8(FP), AX)
CALL ·jumpToKernel(SB)
// Save original state and stack. sysenter() or exception()
// from APP(gr3) will switch to this stack, set the return
// value (vector: 32(SP)) and then do RET, which will also
// automatically return to the lower half.
MOVQ cpu+0(FP), BX
MOVQ regs+8(FP), AX
MOVQ userCR3+16(FP), CX
MOVQ SP, CPU_REGISTERS+PTRACE_RSP(BX)
MOVQ BP, CPU_REGISTERS+PTRACE_RBP(BX)
@@ -134,9 +147,13 @@ TEXT ·sysret(SB),NOSPLIT,$0-24
// See entry_amd64.go.
TEXT ·iret(SB),NOSPLIT,$0-24
// Save original state.
LOAD_KERNEL_ADDRESS(cpu+0(FP), BX)
LOAD_KERNEL_ADDRESS(regs+8(FP), AX)
CALL ·jumpToKernel(SB)
// Save original state and stack. sysenter() or exception()
// from APP(gr3) will switch to this stack, set the return
// value (vector: 32(SP)) and then do RET, which will also
// automatically return to the lower half.
MOVQ cpu+0(FP), BX
MOVQ regs+8(FP), AX
MOVQ userCR3+16(FP), CX
MOVQ SP, CPU_REGISTERS+PTRACE_RSP(BX)
MOVQ BP, CPU_REGISTERS+PTRACE_RBP(BX)
pkg/sentry/platform/ring0/kernel_amd64.go
-2
View File
@@ -197,13 +197,11 @@ func (c *CPU) SwitchToUser(switchOpts SwitchOpts) (vector Vector) {
WriteFS(uintptr(regs.Fs_base)) // escapes: no. Set application FS.
WriteGS(uintptr(regs.Gs_base)) // escapes: no. Set application GS.
LoadFloatingPoint(switchOpts.FloatingPointState) // escapes: no. Copy in floating point.
jumpToKernel() // Switch to upper half.
if switchOpts.FullRestore {
vector = iret(c, regs, uintptr(userCR3))
} else {
vector = sysret(c, regs, uintptr(userCR3))
}
jumpToUser() // Return to lower half.
SaveFloatingPoint(switchOpts.FloatingPointState) // escapes: no. Copy out floating point.
WriteFS(uintptr(c.registers.Fs_base)) // escapes: no. Restore kernel FS.
return
pkg/sentry/platform/ring0/lib_amd64.go
-6
View File
@@ -64,12 +64,6 @@ func wrgsmsr(addr uintptr)
// readCR2 reads the current CR2 value.
func readCR2() uintptr
// jumpToKernel jumps to the kernel version of the current RIP.
func jumpToKernel()
// jumpToUser jumps to the user version of the current RIP.
func jumpToUser()
// fninit initializes the floating point unit.
func fninit()
pkg/sentry/platform/ring0/lib_amd64.s
-25
View File
@@ -127,31 +127,6 @@ TEXT ·wrgsmsr(SB),NOSPLIT,$0-8
BYTE $0x0f; BYTE $0x30; // WRMSR
RET
// jumpToUser changes execution to the user address.
//
// This works by changing the return value to the user version.
TEXT ·jumpToUser(SB),NOSPLIT,$0
MOVQ 0(SP), AX
MOVQ ·KernelStartAddress(SB), BX
NOTQ BX
ANDQ BX, SP // Switch the stack.
ANDQ BX, BP // Switch the frame pointer.
ANDQ BX, AX // Future return value.
MOVQ AX, 0(SP)
RET
// jumpToKernel changes execution to the kernel address space.
//
// This works by changing the return value to the kernel version.
TEXT ·jumpToKernel(SB),NOSPLIT,$0
MOVQ 0(SP), AX
MOVQ ·KernelStartAddress(SB), BX
ORQ BX, SP // Switch the stack.
ORQ BX, BP // Switch the frame pointer.
ORQ BX, AX // Future return value.
MOVQ AX, 0(SP)
RET
// readCR2 reads the current CR2 value.
//
// The code corresponds to: