[v3,49/75] x86/sev-es: Handle instruction fetches from user-space
diff mbox series

Message ID 20200428151725.31091-50-joro@8bytes.org
State New
Headers show
Series
  • x86: SEV-ES Guest Support
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Commit Message

Joerg Roedel April 28, 2020, 3:16 p.m. UTC
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
vc_decode_insn() to safely fetch kernel and user instructions.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kernel/sev-es.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

Comments

Borislav Petkov May 23, 2020, 9:23 a.m. UTC | #1
On Tue, Apr 28, 2020 at 05:16:59PM +0200, Joerg Roedel wrote:
> 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
> vc_decode_insn() to safely fetch kernel and user instructions.
> 
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>  arch/x86/kernel/sev-es.c | 31 ++++++++++++++++++++++---------
>  1 file changed, 22 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> index 85027fb4177e..c2223c2a28c2 100644
> --- a/arch/x86/kernel/sev-es.c
> +++ b/arch/x86/kernel/sev-es.c
> @@ -165,17 +165,30 @@ static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
>  	enum es_result ret;
>  	int res;
>  
> -	res = vc_fetch_insn_kernel(ctxt, buffer);
> -	if (unlikely(res == -EFAULT)) {

Let's also test for 0 in case the probe_read* guts get changed and start
returning so other errval besides -EFAULT.

> -		ctxt->fi.vector     = X86_TRAP_PF;
> -		ctxt->fi.error_code = 0;
> -		ctxt->fi.cr2        = ctxt->regs->ip;
> -		return ES_EXCEPTION;
> +	if (!user_mode(ctxt->regs)) {

Flip that check so that it reads more naturally:

	if (user_mode(..)
			insn_fetch_from_user()

		...
	} else {
		vc_fetch_insn_kernel()

	}

> +		res = vc_fetch_insn_kernel(ctxt, buffer);



> +		if (unlikely(res == -EFAULT)) {
> +			ctxt->fi.vector     = X86_TRAP_PF;
> +			ctxt->fi.error_code = 0;
> +			ctxt->fi.cr2        = ctxt->regs->ip;
> +			return ES_EXCEPTION;
> +		}
> +
> +		insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
> +		insn_get_length(&ctxt->insn);
> +	} else {
> +		res = insn_fetch_from_user(ctxt->regs, buffer);
> +		if (res == 0) {

		if (!res)

Patch
diff mbox series

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 85027fb4177e..c2223c2a28c2 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -165,17 +165,30 @@  static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
 	enum es_result ret;
 	int res;
 
-	res = vc_fetch_insn_kernel(ctxt, buffer);
-	if (unlikely(res == -EFAULT)) {
-		ctxt->fi.vector     = X86_TRAP_PF;
-		ctxt->fi.error_code = 0;
-		ctxt->fi.cr2        = ctxt->regs->ip;
-		return ES_EXCEPTION;
+	if (!user_mode(ctxt->regs)) {
+		res = vc_fetch_insn_kernel(ctxt, buffer);
+		if (unlikely(res == -EFAULT)) {
+			ctxt->fi.vector     = X86_TRAP_PF;
+			ctxt->fi.error_code = 0;
+			ctxt->fi.cr2        = ctxt->regs->ip;
+			return ES_EXCEPTION;
+		}
+
+		insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
+		insn_get_length(&ctxt->insn);
+	} else {
+		res = insn_fetch_from_user(ctxt->regs, buffer);
+		if (res == 0) {
+			ctxt->fi.vector     = X86_TRAP_PF;
+			ctxt->fi.cr2        = ctxt->regs->ip;
+			ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
+			return ES_EXCEPTION;
+		}
+
+		if (!insn_decode(ctxt->regs, &ctxt->insn, buffer, res))
+			return ES_DECODE_FAILED;
 	}
 
-	insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
-	insn_get_length(&ctxt->insn);
-
 	ret = ctxt->insn.immediate.got ? ES_OK : ES_DECODE_FAILED;
 
 	return ret;