[PATCH 50/70] x86/sev-es: Handle DR7 read/write events

Joerg Roedel
2020-03-19T09:16:48Z

From: Tom Lendacky <thomas.lendacky@amd.com>

Add code to handle #VC exceptions on DR7 register reads and writes.
This is needed early because show_regs() reads DR7 to print it out.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
[ jroedel@suse.de: - Adapt to #VC handling framework
- Support early usage ]
Co-developed-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/kernel/sev-es.c | 87 ++++++++++++++++++++++++++++++++++++++--
1 file changed, 83 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 163b8a7f98a4..7a9cdc660637 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -23,6 +23,8 @@
#include <asm/traps.h>
#include <asm/svm.h>

+#define DR7_RESET_VALUE 0x400
+
/* For early boot hypervisor communication in SEV-ES enabled guests */
struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);

@@ -31,6 +33,7 @@ struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);
* cleared
*/
struct ghcb __initdata *boot_ghcb;
+static DEFINE_PER_CPU(unsigned long, cached_dr7) = DR7_RESET_VALUE;

struct ghcb_state {
struct ghcb *ghcb;
@@ -359,6 +362,21 @@ static long *vc_insn_get_reg(struct es_em_ctxt *ctxt)
return reg_array + offset;
}

+static long *vc_insn_get_rm(struct es_em_ctxt *ctxt)
+{
+ long *reg_array;
+ int offset;
+
+ reg_array = (long *)ctxt->regs;
+ offset = insn_get_modrm_rm_off(&ctxt->insn, ctxt->regs);
+
+ if (offset < 0)
+ return NULL;
+
+ offset /= sizeof(long);
+
+ return reg_array + offset;
+}
static enum es_result vc_do_mmio(struct ghcb *ghcb, struct es_em_ctxt *ctxt,
unsigned int bytes, bool read)
{
@@ -587,13 +605,74 @@ static enum es_result vc_handle_mmio(struct ghcb *ghcb,
return ret;
}

+static enum es_result vc_handle_dr7_write(struct ghcb *ghcb,
+ struct es_em_ctxt *ctxt,
+ bool early)
+{
+ long val, *reg = vc_insn_get_rm(ctxt);
+ enum es_result ret;
+
+ if (!reg)
+ return ES_DECODE_FAILED;
+
+ val = *reg;
+
+ /* Upper 32 bits must be written as zeroes */
+ if (val >> 32) {
+ ctxt->fi.vector = X86_TRAP_GP;
+ ctxt->fi.error_code = 0;
+ return ES_EXCEPTION;
+ }
+
+ /* Clear out other reservered bits and set bit 10 */
+ val = (val & 0xffff23ffL) | BIT(10);
+
+ /* Early non-zero writes to DR7 are not supported */
+ if (early && (val & ~DR7_RESET_VALUE))
+ return ES_UNSUPPORTED;
+
+ /* Using a value of 0 for ExitInfo1 means RAX holds the value */
+ ghcb_set_rax(ghcb, val);
+ ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_WRITE_DR7, 0, 0);
+ if (ret != ES_OK)
+ return ret;
+
+ this_cpu_write(cached_dr7, *reg);
+
+ return ES_OK;
+}
+
+static enum es_result vc_handle_dr7_read(struct ghcb *ghcb,
+ struct es_em_ctxt *ctxt,
+ bool early)
+{
+ long *reg = vc_insn_get_rm(ctxt);
+
+ if (!reg)
+ return ES_DECODE_FAILED;
+
+ if (early)
+ *reg = DR7_RESET_VALUE;
+ else
+ *reg = this_cpu_read(cached_dr7);
+
+ return ES_OK;
+}
+
static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
- struct ghcb *ghcb,
- unsigned long exit_code)
+ struct ghcb *ghcb,
+ unsigned long exit_code,
+ bool early)
{
enum es_result result;

switch (exit_code) {
+ case SVM_EXIT_READ_DR7:
+ result = vc_handle_dr7_read(ghcb, ctxt, early);
+ break;
+ case SVM_EXIT_WRITE_DR7:
+ result = vc_handle_dr7_write(ghcb, ctxt, early);
+ break;
case SVM_EXIT_CPUID:
result = vc_handle_cpuid(ghcb, ctxt);
break;
@@ -682,7 +761,7 @@ dotraplinkage void do_vmm_communication(struct pt_regs *regs, unsigned long exit
result = vc_context_filter(regs, exit_code);

if (result == ES_OK)
- result = vc_handle_exitcode(&ctxt, ghcb, exit_code);
+ result = vc_handle_exitcode(&ctxt, ghcb, exit_code, false);

sev_es_put_ghcb(&state);

@@ -750,7 +829,7 @@ bool __init boot_vc_exception(struct pt_regs *regs)
result = vc_init_em_ctxt(&ctxt, regs, exit_code);

if (result == ES_OK)
- result = vc_handle_exitcode(&ctxt, boot_ghcb, exit_code);
+ result = vc_handle_exitcode(&ctxt, boot_ghcb, exit_code, true);

/* Done - now check the result */
switch (result) {
--
2.17.1