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Subject[PATCH 38/62] x86/sev-es: Handle instruction fetches from user-space
Date
From: Joerg Roedel <jroedel@suse.de>

When a #VC exception is triggered by user-space the instruction
decoder needs to read the instruction bytes from user addresses.
Enhance es_fetch_insn_byte() to safely fetch kernel and user
instruction bytes.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/kernel/sev-es.c | 30 +++++++++++++++++++++++-------
1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 2a801919e7c0..f5bff4219f6f 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -61,13 +61,29 @@ static enum es_result es_fetch_insn_byte(struct es_em_ctxt *ctxt,
unsigned int offset,
char *buffer)
{
- char *rip = (char *)ctxt->regs->ip;
-
- /* More checks are needed when we boot to user-space */
- if (!check_kernel(ctxt->regs))
- return ES_UNSUPPORTED;
-
- buffer[offset] = rip[offset];
+ if (user_mode(ctxt->regs)) {
+ unsigned long addr = ctxt->regs->ip + offset;
+ char __user *rip = (char __user *)addr;
+
+ if (unlikely(addr >= TASK_SIZE_MAX))
+ return ES_UNSUPPORTED;
+
+ if (copy_from_user(buffer + offset, rip, 1)) {
+ ctxt->fi.vector = X86_TRAP_PF;
+ ctxt->fi.cr2 = addr;
+ ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
+ return ES_EXCEPTION;
+ }
+ } else {
+ char *rip = (char *)ctxt->regs->ip + offset;
+
+ if (probe_kernel_read(buffer + offset, rip, 1) != 0) {
+ ctxt->fi.vector = X86_TRAP_PF;
+ ctxt->fi.cr2 = (unsigned long)rip;
+ ctxt->fi.error_code = X86_PF_INSTR;
+ return ES_EXCEPTION;
+ }
+ }

return ES_OK;
}
--
2.17.1
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